Hi all,
this is basically a evolution of the series Matthew Wilcox originally
set in June. Based on comments from Jan a Brian this now actually
untangles some of the more confusing conditional in the writeback code
before refactoring it into the iterator. Because of that all the
later patches need a fair amount of rebasing and I've not carried any
reviewed-by over.
The original cover letter is below:
Dave Howells doesn't like the indirect function call imposed by
write_cache_pages(), so refactor it into an iterator. I took the
opportunity to add the ability to iterate a folio_batch without having
an external variable.
This is against next-20230623. If you try to apply it on top of a tree
which doesn't include the pagevec removal series, IT WILL CRASH because
it won't reinitialise folio_batch->i and the iteration will index out
of bounds.
I have a feeling the 'done' parameter could have a better name, but I
can't think what it might be.
Changes since v3:
- various commit log spelling fixes
- remove a statement from a commit log that isn't true any more with the
changes in v3
- rename a function
- merge two helpers
Diffstat:
include/linux/pagevec.h | 18 ++
include/linux/writeback.h | 19 ++
mm/page-writeback.c | 328 +++++++++++++++++++++++++---------------------
3 files changed, 215 insertions(+), 150 deletions(-)
mapping->writeback_index is only [1] used as the starting point for
range_cyclic writeback, so there is no point in updating it for other
types of writeback.
[1] except for btrfs_defrag_file which does really odd things with
mapping->writeback_index. But btrfs doesn't use write_cache_pages at
all, so this isn't relevant here.
Signed-off-by: Christoph Hellwig <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Acked-by: Dave Chinner <[email protected]>
---
mm/page-writeback.c | 24 ++++++++++++++----------
1 file changed, 14 insertions(+), 10 deletions(-)
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 7ed6c2bc8dd51c..c798c0d6d0abb4 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2403,7 +2403,6 @@ int write_cache_pages(struct address_space *mapping,
pgoff_t index;
pgoff_t end; /* Inclusive */
pgoff_t done_index;
- int range_whole = 0;
xa_mark_t tag;
folio_batch_init(&fbatch);
@@ -2413,8 +2412,6 @@ int write_cache_pages(struct address_space *mapping,
} else {
index = wbc->range_start >> PAGE_SHIFT;
end = wbc->range_end >> PAGE_SHIFT;
- if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
- range_whole = 1;
}
if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages) {
tag_pages_for_writeback(mapping, index, end);
@@ -2514,14 +2511,21 @@ int write_cache_pages(struct address_space *mapping,
}
/*
- * If we hit the last page and there is more work to be done: wrap
- * back the index back to the start of the file for the next
- * time we are called.
+ * For range cyclic writeback we need to remember where we stopped so
+ * that we can continue there next time we are called. If we hit the
+ * last page and there is more work to be done, wrap back to the start
+ * of the file.
+ *
+ * For non-cyclic writeback we always start looking up at the beginning
+ * of the file if we are called again, which can only happen due to
+ * -ENOMEM from the file system.
*/
- if (wbc->range_cyclic && !done)
- done_index = 0;
- if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
- mapping->writeback_index = done_index;
+ if (wbc->range_cyclic) {
+ if (done)
+ mapping->writeback_index = done_index;
+ else
+ mapping->writeback_index = 0;
+ }
return ret;
}
--
2.39.2
When write_cache_pages finishes writing out a folio, it fails to update
done_index to account for the number of pages in the folio just written.
That means when range_cyclic writeback is restarted, it will be
restarted at this folio instead of after it as it should. Fix that
by updating done_index before breaking out of the loop.
Signed-off-by: Christoph Hellwig <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Acked-by: Dave Chinner <[email protected]>
---
mm/page-writeback.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index ee2fd6a6af4072..b13ea243edb6b2 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2505,6 +2505,7 @@ int write_cache_pages(struct address_space *mapping,
* keep going until we have written all the pages
* we tagged for writeback prior to entering this loop.
*/
+ done_index = folio->index + nr;
wbc->nr_to_write -= nr;
if (wbc->nr_to_write <= 0 &&
wbc->sync_mode == WB_SYNC_NONE) {
--
2.39.2
From: "Matthew Wilcox (Oracle)" <[email protected]>
Instead of having a 'done' variable that controls the nested loops,
have a writeback_finish() that can be returned directly. This involves
keeping more things in writeback_control, but it's just moving stuff
allocated on the stack to being allocated slightly earlier on the stack.
Signed-off-by: Matthew Wilcox (Oracle) <[email protected]>
[hch: heavily rebased, reordered and commented struct writeback_control]
Signed-off-by: Christoph Hellwig <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Acked-by: Dave Chinner <[email protected]>
---
include/linux/writeback.h | 6 +++
mm/page-writeback.c | 79 ++++++++++++++++++++-------------------
2 files changed, 47 insertions(+), 38 deletions(-)
diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index 833ec38fc3e0c9..390f2dd03cf27e 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -11,6 +11,7 @@
#include <linux/flex_proportions.h>
#include <linux/backing-dev-defs.h>
#include <linux/blk_types.h>
+#include <linux/pagevec.h>
struct bio;
@@ -40,6 +41,7 @@ enum writeback_sync_modes {
* in a manner such that unspecified fields are set to zero.
*/
struct writeback_control {
+ /* public fields that can be set and/or consumed by the caller: */
long nr_to_write; /* Write this many pages, and decrement
this for each page written */
long pages_skipped; /* Pages which were not written */
@@ -77,6 +79,10 @@ struct writeback_control {
*/
struct swap_iocb **swap_plug;
+ /* internal fields used by the ->writepages implementation: */
+ struct folio_batch fbatch;
+ int err;
+
#ifdef CONFIG_CGROUP_WRITEBACK
struct bdi_writeback *wb; /* wb this writeback is issued under */
struct inode *inode; /* inode being written out */
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index c798c0d6d0abb4..564d5faf562ba7 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2360,6 +2360,29 @@ void tag_pages_for_writeback(struct address_space *mapping,
}
EXPORT_SYMBOL(tag_pages_for_writeback);
+static void writeback_finish(struct address_space *mapping,
+ struct writeback_control *wbc, pgoff_t done_index)
+{
+ folio_batch_release(&wbc->fbatch);
+
+ /*
+ * For range cyclic writeback we need to remember where we stopped so
+ * that we can continue there next time we are called. If we hit the
+ * last page and there is more work to be done, wrap back to the start
+ * of the file.
+ *
+ * For non-cyclic writeback we always start looking up at the beginning
+ * of the file if we are called again, which can only happen due to
+ * -ENOMEM from the file system.
+ */
+ if (wbc->range_cyclic) {
+ if (wbc->err || wbc->nr_to_write <= 0)
+ mapping->writeback_index = done_index;
+ else
+ mapping->writeback_index = 0;
+ }
+}
+
/**
* write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
* @mapping: address space structure to write
@@ -2395,17 +2418,12 @@ int write_cache_pages(struct address_space *mapping,
struct writeback_control *wbc, writepage_t writepage,
void *data)
{
- int ret = 0;
- int done = 0;
int error;
- struct folio_batch fbatch;
int nr_folios;
pgoff_t index;
pgoff_t end; /* Inclusive */
- pgoff_t done_index;
xa_mark_t tag;
- folio_batch_init(&fbatch);
if (wbc->range_cyclic) {
index = mapping->writeback_index; /* prev offset */
end = -1;
@@ -2419,22 +2437,23 @@ int write_cache_pages(struct address_space *mapping,
} else {
tag = PAGECACHE_TAG_DIRTY;
}
- done_index = index;
- while (!done && (index <= end)) {
+
+ folio_batch_init(&wbc->fbatch);
+ wbc->err = 0;
+
+ while (index <= end) {
int i;
nr_folios = filemap_get_folios_tag(mapping, &index, end,
- tag, &fbatch);
+ tag, &wbc->fbatch);
if (nr_folios == 0)
break;
for (i = 0; i < nr_folios; i++) {
- struct folio *folio = fbatch.folios[i];
+ struct folio *folio = wbc->fbatch.folios[i];
unsigned long nr;
- done_index = folio->index;
-
folio_lock(folio);
/*
@@ -2481,6 +2500,9 @@ int write_cache_pages(struct address_space *mapping,
folio_unlock(folio);
error = 0;
}
+
+ if (error && !wbc->err)
+ wbc->err = error;
/*
* For integrity sync we have to keep going until we
@@ -2496,38 +2518,19 @@ int write_cache_pages(struct address_space *mapping,
* off and media errors won't choke writeout for the
* entire file.
*/
- if (error && !ret)
- ret = error;
- if (wbc->sync_mode == WB_SYNC_NONE) {
- if (ret || wbc->nr_to_write <= 0) {
- done_index = folio->index + nr;
- done = 1;
- break;
- }
+ if (wbc->sync_mode == WB_SYNC_NONE &&
+ (wbc->err || wbc->nr_to_write <= 0)) {
+ writeback_finish(mapping, wbc,
+ folio->index + nr);
+ return error;
}
}
- folio_batch_release(&fbatch);
+ folio_batch_release(&wbc->fbatch);
cond_resched();
}
- /*
- * For range cyclic writeback we need to remember where we stopped so
- * that we can continue there next time we are called. If we hit the
- * last page and there is more work to be done, wrap back to the start
- * of the file.
- *
- * For non-cyclic writeback we always start looking up at the beginning
- * of the file if we are called again, which can only happen due to
- * -ENOMEM from the file system.
- */
- if (wbc->range_cyclic) {
- if (done)
- mapping->writeback_index = done_index;
- else
- mapping->writeback_index = 0;
- }
-
- return ret;
+ writeback_finish(mapping, wbc, 0);
+ return 0;
}
EXPORT_SYMBOL(write_cache_pages);
--
2.39.2
From: "Matthew Wilcox (Oracle)" <[email protected]>
Signed-off-by: Christoph Hellwig <[email protected]>
[hch: split from a larger patch]
Signed-off-by: Matthew Wilcox (Oracle) <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Acked-by: Dave Chinner <[email protected]>
---
include/linux/writeback.h | 2 --
1 file changed, 2 deletions(-)
diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index 083387c00f0c8b..833ec38fc3e0c9 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -364,8 +364,6 @@ bool wb_over_bg_thresh(struct bdi_writeback *wb);
typedef int (*writepage_t)(struct folio *folio, struct writeback_control *wbc,
void *data);
-void tag_pages_for_writeback(struct address_space *mapping,
- pgoff_t start, pgoff_t end);
int write_cache_pages(struct address_space *mapping,
struct writeback_control *wbc, writepage_t writepage,
void *data);
--
2.39.2
From: "Matthew Wilcox (Oracle)" <[email protected]>
This simple helper will be the basis of the writeback iterator.
To make this work, we need to remember the current index
and end positions in writeback_control.
Signed-off-by: Matthew Wilcox (Oracle) <[email protected]>
[hch: heavily rebased, add helpers to get the tag and end index,
don't keep the end index in struct writeback_control]
Signed-off-by: Christoph Hellwig <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Acked-by: Dave Chinner <[email protected]>
---
include/linux/writeback.h | 1 +
mm/page-writeback.c | 49 +++++++++++++++++++++++++--------------
2 files changed, 32 insertions(+), 18 deletions(-)
diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index 390f2dd03cf27e..195393981ccb5c 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -81,6 +81,7 @@ struct writeback_control {
/* internal fields used by the ->writepages implementation: */
struct folio_batch fbatch;
+ pgoff_t index;
int err;
#ifdef CONFIG_CGROUP_WRITEBACK
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 564d5faf562ba7..798e5264dc0353 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2383,6 +2383,29 @@ static void writeback_finish(struct address_space *mapping,
}
}
+static xa_mark_t wbc_to_tag(struct writeback_control *wbc)
+{
+ if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
+ return PAGECACHE_TAG_TOWRITE;
+ return PAGECACHE_TAG_DIRTY;
+}
+
+static pgoff_t wbc_end(struct writeback_control *wbc)
+{
+ if (wbc->range_cyclic)
+ return -1;
+ return wbc->range_end >> PAGE_SHIFT;
+}
+
+static void writeback_get_batch(struct address_space *mapping,
+ struct writeback_control *wbc)
+{
+ folio_batch_release(&wbc->fbatch);
+ cond_resched();
+ filemap_get_folios_tag(mapping, &wbc->index, wbc_end(wbc),
+ wbc_to_tag(wbc), &wbc->fbatch);
+}
+
/**
* write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
* @mapping: address space structure to write
@@ -2419,38 +2442,30 @@ int write_cache_pages(struct address_space *mapping,
void *data)
{
int error;
- int nr_folios;
- pgoff_t index;
pgoff_t end; /* Inclusive */
- xa_mark_t tag;
if (wbc->range_cyclic) {
- index = mapping->writeback_index; /* prev offset */
+ wbc->index = mapping->writeback_index; /* prev offset */
end = -1;
} else {
- index = wbc->range_start >> PAGE_SHIFT;
+ wbc->index = wbc->range_start >> PAGE_SHIFT;
end = wbc->range_end >> PAGE_SHIFT;
}
- if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages) {
- tag_pages_for_writeback(mapping, index, end);
- tag = PAGECACHE_TAG_TOWRITE;
- } else {
- tag = PAGECACHE_TAG_DIRTY;
- }
+ if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
+ tag_pages_for_writeback(mapping, wbc->index, end);
folio_batch_init(&wbc->fbatch);
wbc->err = 0;
- while (index <= end) {
+ while (wbc->index <= end) {
int i;
- nr_folios = filemap_get_folios_tag(mapping, &index, end,
- tag, &wbc->fbatch);
+ writeback_get_batch(mapping, wbc);
- if (nr_folios == 0)
+ if (wbc->fbatch.nr == 0)
break;
- for (i = 0; i < nr_folios; i++) {
+ for (i = 0; i < wbc->fbatch.nr; i++) {
struct folio *folio = wbc->fbatch.folios[i];
unsigned long nr;
@@ -2525,8 +2540,6 @@ int write_cache_pages(struct address_space *mapping,
return error;
}
}
- folio_batch_release(&wbc->fbatch);
- cond_resched();
}
writeback_finish(mapping, wbc, 0);
--
2.39.2
From: "Matthew Wilcox (Oracle)" <[email protected]>
Add a loop counter inside the folio_batch to let us iterate from 0-nr
instead of decrementing nr and treating the batch as a stack. It would
generate some very weird and suboptimal I/O patterns for page writeback
to iterate over the batch as a stack.
Signed-off-by: Matthew Wilcox (Oracle) <[email protected]>
Signed-off-by: Christoph Hellwig <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Acked-by: Dave Chinner <[email protected]>
---
include/linux/pagevec.h | 18 ++++++++++++++++++
1 file changed, 18 insertions(+)
diff --git a/include/linux/pagevec.h b/include/linux/pagevec.h
index 87cc678adc850b..fcc06c300a72c3 100644
--- a/include/linux/pagevec.h
+++ b/include/linux/pagevec.h
@@ -27,6 +27,7 @@ struct folio;
*/
struct folio_batch {
unsigned char nr;
+ unsigned char i;
bool percpu_pvec_drained;
struct folio *folios[PAGEVEC_SIZE];
};
@@ -40,12 +41,14 @@ struct folio_batch {
static inline void folio_batch_init(struct folio_batch *fbatch)
{
fbatch->nr = 0;
+ fbatch->i = 0;
fbatch->percpu_pvec_drained = false;
}
static inline void folio_batch_reinit(struct folio_batch *fbatch)
{
fbatch->nr = 0;
+ fbatch->i = 0;
}
static inline unsigned int folio_batch_count(struct folio_batch *fbatch)
@@ -75,6 +78,21 @@ static inline unsigned folio_batch_add(struct folio_batch *fbatch,
return folio_batch_space(fbatch);
}
+/**
+ * folio_batch_next - Return the next folio to process.
+ * @fbatch: The folio batch being processed.
+ *
+ * Use this function to implement a queue of folios.
+ *
+ * Return: The next folio in the queue, or NULL if the queue is empty.
+ */
+static inline struct folio *folio_batch_next(struct folio_batch *fbatch)
+{
+ if (fbatch->i == fbatch->nr)
+ return NULL;
+ return fbatch->folios[fbatch->i++];
+}
+
void __folio_batch_release(struct folio_batch *pvec);
static inline void folio_batch_release(struct folio_batch *fbatch)
--
2.39.2
Rework the way we deal with the cleanup after the writepage call.
First handle the magic AOP_WRITEPAGE_ACTIVATE separately from real error
returns to get it out of the way of the actual error handling path.
Then merge the code to set ret for integrity vs non-integrity writeback.
For non-integrity writeback the loop is terminated on the first error, so
ret will never be non-zero. Then use a single block to check for
non-integrity writewack to consolidate the cases where it returns for
either an error or running off the end of nr_to_write.
Signed-off-by: Christoph Hellwig <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Acked-by: Dave Chinner <[email protected]>
---
mm/page-writeback.c | 62 +++++++++++++++++++++------------------------
1 file changed, 29 insertions(+), 33 deletions(-)
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 8e312d73475646..7ed6c2bc8dd51c 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2474,43 +2474,39 @@ int write_cache_pages(struct address_space *mapping,
error = writepage(folio, wbc, data);
nr = folio_nr_pages(folio);
wbc->nr_to_write -= nr;
- if (unlikely(error)) {
- /*
- * Handle errors according to the type of
- * writeback. There's no need to continue for
- * background writeback. Just push done_index
- * past this page so media errors won't choke
- * writeout for the entire file. For integrity
- * writeback, we must process the entire dirty
- * set regardless of errors because the fs may
- * still have state to clear for each page. In
- * that case we continue processing and return
- * the first error.
- */
- if (error == AOP_WRITEPAGE_ACTIVATE) {
- folio_unlock(folio);
- error = 0;
- } else if (wbc->sync_mode != WB_SYNC_ALL) {
- ret = error;
- done_index = folio->index + nr;
- done = 1;
- break;
- }
- if (!ret)
- ret = error;
+
+ /*
+ * Handle the legacy AOP_WRITEPAGE_ACTIVATE magic return
+ * value. Eventually all instances should just unlock
+ * the folio themselves and return 0;
+ */
+ if (error == AOP_WRITEPAGE_ACTIVATE) {
+ folio_unlock(folio);
+ error = 0;
}
/*
- * We stop writing back only if we are not doing
- * integrity sync. In case of integrity sync we have to
- * keep going until we have written all the pages
- * we tagged for writeback prior to entering this loop.
+ * For integrity sync we have to keep going until we
+ * have written all the folios we tagged for writeback
+ * prior to entering this loop, even if we run past
+ * wbc->nr_to_write or encounter errors. This is
+ * because the file system may still have state to clear
+ * for each folio. We'll eventually return the first
+ * error encountered.
+ *
+ * For background writeback just push done_index past
+ * this folio so that we can just restart where we left
+ * off and media errors won't choke writeout for the
+ * entire file.
*/
- done_index = folio->index + nr;
- if (wbc->nr_to_write <= 0 &&
- wbc->sync_mode == WB_SYNC_NONE) {
- done = 1;
- break;
+ if (error && !ret)
+ ret = error;
+ if (wbc->sync_mode == WB_SYNC_NONE) {
+ if (ret || wbc->nr_to_write <= 0) {
+ done_index = folio->index + nr;
+ done = 1;
+ break;
+ }
}
}
folio_batch_release(&fbatch);
--
2.39.2
From: "Matthew Wilcox (Oracle)" <[email protected]>
Reduce write_cache_pages() by about 30 lines; much of it is commentary,
but it all bundles nicely into an obvious function.
Signed-off-by: Matthew Wilcox (Oracle) <[email protected]>
[hch: rename should_writeback_folio to folio_prepare_writeback based on
a comment from Jan Kara]
Signed-off-by: Christoph Hellwig <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Acked-by: Dave Chinner <[email protected]>
---
mm/page-writeback.c | 61 +++++++++++++++++++++++++--------------------
1 file changed, 34 insertions(+), 27 deletions(-)
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 798e5264dc0353..fe508548482217 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2397,6 +2397,38 @@ static pgoff_t wbc_end(struct writeback_control *wbc)
return wbc->range_end >> PAGE_SHIFT;
}
+static bool folio_prepare_writeback(struct address_space *mapping,
+ struct writeback_control *wbc, struct folio *folio)
+{
+ /*
+ * Folio truncated or invalidated. We can freely skip it then,
+ * even for data integrity operations: the folio has disappeared
+ * concurrently, so there could be no real expectation of this
+ * data integrity operation even if there is now a new, dirty
+ * folio at the same pagecache index.
+ */
+ if (unlikely(folio->mapping != mapping))
+ return false;
+
+ /*
+ * Did somebody else write it for us?
+ */
+ if (!folio_test_dirty(folio))
+ return false;
+
+ if (folio_test_writeback(folio)) {
+ if (wbc->sync_mode == WB_SYNC_NONE)
+ return false;
+ folio_wait_writeback(folio);
+ }
+ BUG_ON(folio_test_writeback(folio));
+
+ if (!folio_clear_dirty_for_io(folio))
+ return false;
+
+ return true;
+}
+
static void writeback_get_batch(struct address_space *mapping,
struct writeback_control *wbc)
{
@@ -2470,38 +2502,13 @@ int write_cache_pages(struct address_space *mapping,
unsigned long nr;
folio_lock(folio);
-
- /*
- * Page truncated or invalidated. We can freely skip it
- * then, even for data integrity operations: the page
- * has disappeared concurrently, so there could be no
- * real expectation of this data integrity operation
- * even if there is now a new, dirty page at the same
- * pagecache address.
- */
- if (unlikely(folio->mapping != mapping)) {
-continue_unlock:
+ if (!folio_prepare_writeback(mapping, wbc, folio)) {
folio_unlock(folio);
continue;
}
- if (!folio_test_dirty(folio)) {
- /* someone wrote it for us */
- goto continue_unlock;
- }
-
- if (folio_test_writeback(folio)) {
- if (wbc->sync_mode != WB_SYNC_NONE)
- folio_wait_writeback(folio);
- else
- goto continue_unlock;
- }
-
- BUG_ON(folio_test_writeback(folio));
- if (!folio_clear_dirty_for_io(folio))
- goto continue_unlock;
-
trace_wbc_writepage(wbc, inode_to_bdi(mapping->host));
+
error = writepage(folio, wbc, data);
nr = folio_nr_pages(folio);
wbc->nr_to_write -= nr;
--
2.39.2
From: "Matthew Wilcox (Oracle)" <[email protected]>
Instead of keeping our own local iterator variable, use the one just
added to folio_batch.
Signed-off-by: Matthew Wilcox (Oracle) <[email protected]>
Signed-off-by: Christoph Hellwig <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Acked-by: Dave Chinner <[email protected]>
---
mm/page-writeback.c | 29 +++++++++++++++--------------
1 file changed, 15 insertions(+), 14 deletions(-)
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index d62bc3498ed975..47457895891221 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2429,13 +2429,21 @@ static bool folio_prepare_writeback(struct address_space *mapping,
return true;
}
-static void writeback_get_batch(struct address_space *mapping,
+static struct folio *writeback_get_folio(struct address_space *mapping,
struct writeback_control *wbc)
{
- folio_batch_release(&wbc->fbatch);
- cond_resched();
- filemap_get_folios_tag(mapping, &wbc->index, wbc_end(wbc),
- wbc_to_tag(wbc), &wbc->fbatch);
+ struct folio *folio;
+
+ folio = folio_batch_next(&wbc->fbatch);
+ if (!folio) {
+ folio_batch_release(&wbc->fbatch);
+ cond_resched();
+ filemap_get_folios_tag(mapping, &wbc->index, wbc_end(wbc),
+ wbc_to_tag(wbc), &wbc->fbatch);
+ folio = folio_batch_next(&wbc->fbatch);
+ }
+
+ return folio;
}
/**
@@ -2475,7 +2483,6 @@ int write_cache_pages(struct address_space *mapping,
{
int error;
pgoff_t end; /* Inclusive */
- int i = 0;
if (wbc->range_cyclic) {
wbc->index = mapping->writeback_index; /* prev offset */
@@ -2491,18 +2498,12 @@ int write_cache_pages(struct address_space *mapping,
wbc->err = 0;
for (;;) {
- struct folio *folio;
+ struct folio *folio = writeback_get_folio(mapping, wbc);
unsigned long nr;
- if (i == wbc->fbatch.nr) {
- writeback_get_batch(mapping, wbc);
- i = 0;
- }
- if (wbc->fbatch.nr == 0)
+ if (!folio)
break;
- folio = wbc->fbatch.folios[i++];
-
folio_lock(folio);
if (!folio_prepare_writeback(mapping, wbc, folio)) {
folio_unlock(folio);
--
2.39.2
From: "Matthew Wilcox (Oracle)" <[email protected]>
Make it return the first folio in the batch so that we can use it
in a typical for() pattern.
Signed-off-by: Matthew Wilcox (Oracle) <[email protected]>
Signed-off-by: Christoph Hellwig <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Acked-by: Dave Chinner <[email protected]>
---
mm/page-writeback.c | 39 ++++++++++++++++++++-------------------
1 file changed, 20 insertions(+), 19 deletions(-)
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 47457895891221..f85145f330bb36 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2446,6 +2446,22 @@ static struct folio *writeback_get_folio(struct address_space *mapping,
return folio;
}
+static struct folio *writeback_iter_init(struct address_space *mapping,
+ struct writeback_control *wbc)
+{
+ if (wbc->range_cyclic)
+ wbc->index = mapping->writeback_index; /* prev offset */
+ else
+ wbc->index = wbc->range_start >> PAGE_SHIFT;
+
+ if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
+ tag_pages_for_writeback(mapping, wbc->index, wbc_end(wbc));
+
+ wbc->err = 0;
+ folio_batch_init(&wbc->fbatch);
+ return writeback_get_folio(mapping, wbc);
+}
+
/**
* write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
* @mapping: address space structure to write
@@ -2481,29 +2497,14 @@ int write_cache_pages(struct address_space *mapping,
struct writeback_control *wbc, writepage_t writepage,
void *data)
{
+ struct folio *folio;
int error;
- pgoff_t end; /* Inclusive */
- if (wbc->range_cyclic) {
- wbc->index = mapping->writeback_index; /* prev offset */
- end = -1;
- } else {
- wbc->index = wbc->range_start >> PAGE_SHIFT;
- end = wbc->range_end >> PAGE_SHIFT;
- }
- if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
- tag_pages_for_writeback(mapping, wbc->index, end);
-
- folio_batch_init(&wbc->fbatch);
- wbc->err = 0;
-
- for (;;) {
- struct folio *folio = writeback_get_folio(mapping, wbc);
+ for (folio = writeback_iter_init(mapping, wbc);
+ folio;
+ folio = writeback_get_folio(mapping, wbc)) {
unsigned long nr;
- if (!folio)
- break;
-
folio_lock(folio);
if (!folio_prepare_writeback(mapping, wbc, folio)) {
folio_unlock(folio);
--
2.39.2
From: "Matthew Wilcox (Oracle)" <[email protected]>
Move the loop for should-we-write-this-folio to writeback_get_folio.
Signed-off-by: Matthew Wilcox (Oracle) <[email protected]>
[hch: folded the loop into the existing helper instead of a separate one
as suggested by Jan Kara]
Signed-off-by: Christoph Hellwig <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Acked-by: Dave Chinner <[email protected]>
---
mm/page-writeback.c | 18 ++++++++++--------
1 file changed, 10 insertions(+), 8 deletions(-)
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index f85145f330bb36..b6048c14748fdb 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2434,6 +2434,7 @@ static struct folio *writeback_get_folio(struct address_space *mapping,
{
struct folio *folio;
+retry:
folio = folio_batch_next(&wbc->fbatch);
if (!folio) {
folio_batch_release(&wbc->fbatch);
@@ -2441,8 +2442,17 @@ static struct folio *writeback_get_folio(struct address_space *mapping,
filemap_get_folios_tag(mapping, &wbc->index, wbc_end(wbc),
wbc_to_tag(wbc), &wbc->fbatch);
folio = folio_batch_next(&wbc->fbatch);
+ if (!folio)
+ return NULL;
}
+ folio_lock(folio);
+ if (unlikely(!folio_prepare_writeback(mapping, wbc, folio))) {
+ folio_unlock(folio);
+ goto retry;
+ }
+
+ trace_wbc_writepage(wbc, inode_to_bdi(mapping->host));
return folio;
}
@@ -2505,14 +2515,6 @@ int write_cache_pages(struct address_space *mapping,
folio = writeback_get_folio(mapping, wbc)) {
unsigned long nr;
- folio_lock(folio);
- if (!folio_prepare_writeback(mapping, wbc, folio)) {
- folio_unlock(folio);
- continue;
- }
-
- trace_wbc_writepage(wbc, inode_to_bdi(mapping->host));
-
error = writepage(folio, wbc, data);
nr = folio_nr_pages(folio);
wbc->nr_to_write -= nr;
--
2.39.2
From: "Matthew Wilcox (Oracle)" <[email protected]>
Collapse the two nested loops into one. This is needed as a step
towards turning this into an iterator.
Note that this drops the "index <= end" check in the previous outer loop
and just relies on filemap_get_folios_tag() to return 0 entries when
index > end. This actually has a subtle implication when end == -1
because then the returned index will be -1 as well and thus if there is
page present on index -1, we could be looping indefinitely. But as the
comment in filemap_get_folios_tag documents this as already broken anyway
we should not worry about it here either. The fix for that would
probably a change to the filemap_get_folios_tag() calling convention.
Signed-off-by: Matthew Wilcox (Oracle) <[email protected]>
[hch: updated the commit log based on feedback from Jan Kara]
Signed-off-by: Christoph Hellwig <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Acked-by: Dave Chinner <[email protected]>
---
mm/page-writeback.c | 94 ++++++++++++++++++++++-----------------------
1 file changed, 46 insertions(+), 48 deletions(-)
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index fe508548482217..d62bc3498ed975 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2475,6 +2475,7 @@ int write_cache_pages(struct address_space *mapping,
{
int error;
pgoff_t end; /* Inclusive */
+ int i = 0;
if (wbc->range_cyclic) {
wbc->index = mapping->writeback_index; /* prev offset */
@@ -2489,63 +2490,60 @@ int write_cache_pages(struct address_space *mapping,
folio_batch_init(&wbc->fbatch);
wbc->err = 0;
- while (wbc->index <= end) {
- int i;
-
- writeback_get_batch(mapping, wbc);
+ for (;;) {
+ struct folio *folio;
+ unsigned long nr;
+ if (i == wbc->fbatch.nr) {
+ writeback_get_batch(mapping, wbc);
+ i = 0;
+ }
if (wbc->fbatch.nr == 0)
break;
- for (i = 0; i < wbc->fbatch.nr; i++) {
- struct folio *folio = wbc->fbatch.folios[i];
- unsigned long nr;
+ folio = wbc->fbatch.folios[i++];
- folio_lock(folio);
- if (!folio_prepare_writeback(mapping, wbc, folio)) {
- folio_unlock(folio);
- continue;
- }
+ folio_lock(folio);
+ if (!folio_prepare_writeback(mapping, wbc, folio)) {
+ folio_unlock(folio);
+ continue;
+ }
- trace_wbc_writepage(wbc, inode_to_bdi(mapping->host));
+ trace_wbc_writepage(wbc, inode_to_bdi(mapping->host));
- error = writepage(folio, wbc, data);
- nr = folio_nr_pages(folio);
- wbc->nr_to_write -= nr;
+ error = writepage(folio, wbc, data);
+ nr = folio_nr_pages(folio);
+ wbc->nr_to_write -= nr;
- /*
- * Handle the legacy AOP_WRITEPAGE_ACTIVATE magic return
- * value. Eventually all instances should just unlock
- * the folio themselves and return 0;
- */
- if (error == AOP_WRITEPAGE_ACTIVATE) {
- folio_unlock(folio);
- error = 0;
- }
-
- if (error && !wbc->err)
- wbc->err = error;
+ /*
+ * Handle the legacy AOP_WRITEPAGE_ACTIVATE magic return value.
+ * Eventually all instances should just unlock the folio
+ * themselves and return 0;
+ */
+ if (error == AOP_WRITEPAGE_ACTIVATE) {
+ folio_unlock(folio);
+ error = 0;
+ }
- /*
- * For integrity sync we have to keep going until we
- * have written all the folios we tagged for writeback
- * prior to entering this loop, even if we run past
- * wbc->nr_to_write or encounter errors. This is
- * because the file system may still have state to clear
- * for each folio. We'll eventually return the first
- * error encountered.
- *
- * For background writeback just push done_index past
- * this folio so that we can just restart where we left
- * off and media errors won't choke writeout for the
- * entire file.
- */
- if (wbc->sync_mode == WB_SYNC_NONE &&
- (wbc->err || wbc->nr_to_write <= 0)) {
- writeback_finish(mapping, wbc,
- folio->index + nr);
- return error;
- }
+ if (error && !wbc->err)
+ wbc->err = error;
+
+ /*
+ * For integrity sync we have to keep going until we have
+ * written all the folios we tagged for writeback prior to
+ * entering this loop, even if we run past wbc->nr_to_write or
+ * encounter errors. This is because the file system may still
+ * have state to clear for each folio. We'll eventually return
+ * the first error encountered.
+ *
+ * For background writeback just push done_index past this folio
+ * so that we can just restart where we left off and media
+ * errors won't choke writeout for the entire file.
+ */
+ if (wbc->sync_mode == WB_SYNC_NONE &&
+ (wbc->err || wbc->nr_to_write <= 0)) {
+ writeback_finish(mapping, wbc, folio->index + nr);
+ return error;
}
}
--
2.39.2
From: "Matthew Wilcox (Oracle)" <[email protected]>
Pull the post-processing of the writepage_t callback into a separate
function. That means changing writeback_get_next() to call
writeback_finish() when we naturally run out of folios.
Signed-off-by: Matthew Wilcox (Oracle) <[email protected]>
Signed-off-by: Christoph Hellwig <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Acked-by: Dave Chinner <[email protected]>
---
mm/page-writeback.c | 85 ++++++++++++++++++++++++---------------------
1 file changed, 45 insertions(+), 40 deletions(-)
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index b6048c14748fdb..a041cc563762ae 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2442,8 +2442,10 @@ static struct folio *writeback_get_folio(struct address_space *mapping,
filemap_get_folios_tag(mapping, &wbc->index, wbc_end(wbc),
wbc_to_tag(wbc), &wbc->fbatch);
folio = folio_batch_next(&wbc->fbatch);
- if (!folio)
+ if (!folio) {
+ writeback_finish(mapping, wbc, 0);
return NULL;
+ }
}
folio_lock(folio);
@@ -2472,6 +2474,46 @@ static struct folio *writeback_iter_init(struct address_space *mapping,
return writeback_get_folio(mapping, wbc);
}
+static struct folio *writeback_iter_next(struct address_space *mapping,
+ struct writeback_control *wbc, struct folio *folio, int error)
+{
+ unsigned long nr = folio_nr_pages(folio);
+
+ wbc->nr_to_write -= nr;
+
+ /*
+ * Handle the legacy AOP_WRITEPAGE_ACTIVATE magic return value.
+ * Eventually all instances should just unlock the folio themselves and
+ * return 0;
+ */
+ if (error == AOP_WRITEPAGE_ACTIVATE) {
+ folio_unlock(folio);
+ error = 0;
+ }
+
+ if (error && !wbc->err)
+ wbc->err = error;
+
+ /*
+ * For integrity sync we have to keep going until we have written all
+ * the folios we tagged for writeback prior to entering the writeback
+ * loop, even if we run past wbc->nr_to_write or encounter errors.
+ * This is because the file system may still have state to clear for
+ * each folio. We'll eventually return the first error encountered.
+ *
+ * For background writeback just push done_index past this folio so that
+ * we can just restart where we left off and media errors won't choke
+ * writeout for the entire file.
+ */
+ if (wbc->sync_mode == WB_SYNC_NONE &&
+ (wbc->err || wbc->nr_to_write <= 0)) {
+ writeback_finish(mapping, wbc, folio->index + nr);
+ return NULL;
+ }
+
+ return writeback_get_folio(mapping, wbc);
+}
+
/**
* write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
* @mapping: address space structure to write
@@ -2512,47 +2554,10 @@ int write_cache_pages(struct address_space *mapping,
for (folio = writeback_iter_init(mapping, wbc);
folio;
- folio = writeback_get_folio(mapping, wbc)) {
- unsigned long nr;
-
+ folio = writeback_iter_next(mapping, wbc, folio, error))
error = writepage(folio, wbc, data);
- nr = folio_nr_pages(folio);
- wbc->nr_to_write -= nr;
-
- /*
- * Handle the legacy AOP_WRITEPAGE_ACTIVATE magic return value.
- * Eventually all instances should just unlock the folio
- * themselves and return 0;
- */
- if (error == AOP_WRITEPAGE_ACTIVATE) {
- folio_unlock(folio);
- error = 0;
- }
-
- if (error && !wbc->err)
- wbc->err = error;
- /*
- * For integrity sync we have to keep going until we have
- * written all the folios we tagged for writeback prior to
- * entering this loop, even if we run past wbc->nr_to_write or
- * encounter errors. This is because the file system may still
- * have state to clear for each folio. We'll eventually return
- * the first error encountered.
- *
- * For background writeback just push done_index past this folio
- * so that we can just restart where we left off and media
- * errors won't choke writeout for the entire file.
- */
- if (wbc->sync_mode == WB_SYNC_NONE &&
- (wbc->err || wbc->nr_to_write <= 0)) {
- writeback_finish(mapping, wbc, folio->index + nr);
- return error;
- }
- }
-
- writeback_finish(mapping, wbc, 0);
- return 0;
+ return wbc->err;
}
EXPORT_SYMBOL(write_cache_pages);
--
2.39.2
From: "Matthew Wilcox (Oracle)" <[email protected]>
Wrap up the iterator with a nice bit of syntactic sugar. Now the
caller doesn't need to know about wbc->err and can just return error,
not knowing that the iterator took care of storing errors correctly.
Signed-off-by: Matthew Wilcox (Oracle) <[email protected]>
Signed-off-by: Christoph Hellwig <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Acked-by: Dave Chinner <[email protected]>
---
include/linux/writeback.h | 10 ++++++++++
mm/page-writeback.c | 8 +++-----
2 files changed, 13 insertions(+), 5 deletions(-)
diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index 195393981ccb5c..1c1a543070c17b 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -368,6 +368,16 @@ int balance_dirty_pages_ratelimited_flags(struct address_space *mapping,
bool wb_over_bg_thresh(struct bdi_writeback *wb);
+struct folio *writeback_iter_init(struct address_space *mapping,
+ struct writeback_control *wbc);
+struct folio *writeback_iter_next(struct address_space *mapping,
+ struct writeback_control *wbc, struct folio *folio, int error);
+
+#define for_each_writeback_folio(mapping, wbc, folio, error) \
+ for (folio = writeback_iter_init(mapping, wbc); \
+ folio || ((error = wbc->err), false); \
+ folio = writeback_iter_next(mapping, wbc, folio, error))
+
typedef int (*writepage_t)(struct folio *folio, struct writeback_control *wbc,
void *data);
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index a041cc563762ae..5c33a4a527b3fa 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2458,7 +2458,7 @@ static struct folio *writeback_get_folio(struct address_space *mapping,
return folio;
}
-static struct folio *writeback_iter_init(struct address_space *mapping,
+struct folio *writeback_iter_init(struct address_space *mapping,
struct writeback_control *wbc)
{
if (wbc->range_cyclic)
@@ -2474,7 +2474,7 @@ static struct folio *writeback_iter_init(struct address_space *mapping,
return writeback_get_folio(mapping, wbc);
}
-static struct folio *writeback_iter_next(struct address_space *mapping,
+struct folio *writeback_iter_next(struct address_space *mapping,
struct writeback_control *wbc, struct folio *folio, int error)
{
unsigned long nr = folio_nr_pages(folio);
@@ -2552,9 +2552,7 @@ int write_cache_pages(struct address_space *mapping,
struct folio *folio;
int error;
- for (folio = writeback_iter_init(mapping, wbc);
- folio;
- folio = writeback_iter_next(mapping, wbc, folio, error))
+ for_each_writeback_folio(mapping, wbc, folio, error)
error = writepage(folio, wbc, data);
return wbc->err;
--
2.39.2
When exiting write_cache_pages early due to a non-integrity write
failure, wbc->nr_to_write currently doesn't account for the folio
we just failed to write. This doesn't matter because the callers
always ingore the value on a failure, but moving the update to
common code will allow to simplify the code, so do it.
Signed-off-by: Christoph Hellwig <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Acked-by: Dave Chinner <[email protected]>
---
mm/page-writeback.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index b13ea243edb6b2..8e312d73475646 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2473,6 +2473,7 @@ int write_cache_pages(struct address_space *mapping,
trace_wbc_writepage(wbc, inode_to_bdi(mapping->host));
error = writepage(folio, wbc, data);
nr = folio_nr_pages(folio);
+ wbc->nr_to_write -= nr;
if (unlikely(error)) {
/*
* Handle errors according to the type of
@@ -2506,7 +2507,6 @@ int write_cache_pages(struct address_space *mapping,
* we tagged for writeback prior to entering this loop.
*/
done_index = folio->index + nr;
- wbc->nr_to_write -= nr;
if (wbc->nr_to_write <= 0 &&
wbc->sync_mode == WB_SYNC_NONE) {
done = 1;
--
2.39.2
From: "Matthew Wilcox (Oracle)" <[email protected]>
Use the new for_each_writeback_folio() directly instead of indirecting
through a callback.
Signed-off-by: Matthew Wilcox (Oracle) <[email protected]>
Signed-off-by: Christoph Hellwig <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Acked-by: Dave Chinner <[email protected]>
---
mm/page-writeback.c | 27 +++++++++++++++------------
1 file changed, 15 insertions(+), 12 deletions(-)
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 5c33a4a527b3fa..1ff444d5e4317a 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2559,13 +2559,21 @@ int write_cache_pages(struct address_space *mapping,
}
EXPORT_SYMBOL(write_cache_pages);
-static int writepage_cb(struct folio *folio, struct writeback_control *wbc,
- void *data)
+static int writeback_use_writepage(struct address_space *mapping,
+ struct writeback_control *wbc)
{
- struct address_space *mapping = data;
- int ret = mapping->a_ops->writepage(&folio->page, wbc);
- mapping_set_error(mapping, ret);
- return ret;
+ struct blk_plug plug;
+ struct folio *folio;
+ int err;
+
+ blk_start_plug(&plug);
+ for_each_writeback_folio(mapping, wbc, folio, err) {
+ err = mapping->a_ops->writepage(&folio->page, wbc);
+ mapping_set_error(mapping, err);
+ }
+ blk_finish_plug(&plug);
+
+ return err;
}
int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
@@ -2581,12 +2589,7 @@ int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
if (mapping->a_ops->writepages) {
ret = mapping->a_ops->writepages(mapping, wbc);
} else if (mapping->a_ops->writepage) {
- struct blk_plug plug;
-
- blk_start_plug(&plug);
- ret = write_cache_pages(mapping, wbc, writepage_cb,
- mapping);
- blk_finish_plug(&plug);
+ ret = writeback_use_writepage(mapping, wbc);
} else {
/* deal with chardevs and other special files */
ret = 0;
--
2.39.2
Don't refer to write_cache_pages, which now is just a wrapper for the
writeback iterator.
Signed-off-by: Christoph Hellwig <[email protected]>
Acked-by: Dave Chinner <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
---
mm/page-writeback.c | 14 +++++++-------
1 file changed, 7 insertions(+), 7 deletions(-)
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 1ff444d5e4317a..0546741856d70d 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2325,18 +2325,18 @@ void __init page_writeback_init(void)
}
/**
- * tag_pages_for_writeback - tag pages to be written by write_cache_pages
+ * tag_pages_for_writeback - tag pages to be written by writeback
* @mapping: address space structure to write
* @start: starting page index
* @end: ending page index (inclusive)
*
* This function scans the page range from @start to @end (inclusive) and tags
- * all pages that have DIRTY tag set with a special TOWRITE tag. The idea is
- * that write_cache_pages (or whoever calls this function) will then use
- * TOWRITE tag to identify pages eligible for writeback. This mechanism is
- * used to avoid livelocking of writeback by a process steadily creating new
- * dirty pages in the file (thus it is important for this function to be quick
- * so that it can tag pages faster than a dirtying process can create them).
+ * all pages that have DIRTY tag set with a special TOWRITE tag. The caller
+ * can then use the TOWRITE tag to identify pages eligible for writeback.
+ * This mechanism is used to avoid livelocking of writeback by a process
+ * steadily creating new dirty pages in the file (thus it is important for this
+ * function to be quick so that it can tag pages faster than a dirtying process
+ * can create them).
*/
void tag_pages_for_writeback(struct address_space *mapping,
pgoff_t start, pgoff_t end)
--
2.39.2