Previously, we played around with magical page->mapping for short-lived
temporary pages since we need to identify different types of pages in
the same pcluster but both invalidated and short-lived temporary pages
can have page->mapping == NULL. It was considered as safe because that
temporary pages are all non-LRU / non-movable pages.
This patch tends to use specific page->private to identify short-lived
pages instead so it won't rely on page->mapping anymore. Details are
described in "compress.h" as well.
Reviewed-by: Chao Yu <[email protected]>
Signed-off-by: Gao Xiang <[email protected]>
---
changes since v2:
- use attach_page_private & detach_page_private for managed pages (Chao)
Note that that pattern isn't necessary for all cases, e.g:
1. onlinepages, which hold a page lock, so no need to +/- a ref;
2. shortlivedpages, which are directly from buddy system, no need
to +/- a ref as well.
Detail discussion at
https://lore.kernel.org/r/[email protected]/
fs/erofs/compress.h | 51 ++++++++++++++++++++++++++----------
fs/erofs/decompressor.c | 2 +-
fs/erofs/zdata.c | 57 ++++++++++++++++++++++-------------------
fs/erofs/zdata.h | 1 +
4 files changed, 71 insertions(+), 40 deletions(-)
diff --git a/fs/erofs/compress.h b/fs/erofs/compress.h
index 3d452443c545..4dadde18cdf1 100644
--- a/fs/erofs/compress.h
+++ b/fs/erofs/compress.h
@@ -26,30 +26,55 @@ struct z_erofs_decompress_req {
bool inplace_io, partial_decoding;
};
+/* some special page->private (unsigned long, see below) */
+#define Z_EROFS_SHORTLIVED_PAGE (-1UL << 2)
+
/*
- * - 0x5A110C8D ('sallocated', Z_EROFS_MAPPING_STAGING) -
- * used to mark temporary allocated pages from other
- * file/cached pages and NULL mapping pages.
+ * For all pages in a pcluster, page->private should be one of
+ * Type Last 2bits page->private
+ * short-lived page 00 Z_EROFS_SHORTLIVED_PAGE
+ * cached/managed page 00 pointer to z_erofs_pcluster
+ * online page (file-backed, 01/10/11 sub-index << 2 | count
+ * some pages can be used for inplace I/O)
+ *
+ * page->mapping should be one of
+ * Type page->mapping
+ * short-lived page NULL
+ * cached/managed page non-NULL or NULL (invalidated/truncated page)
+ * online page non-NULL
+ *
+ * For all managed pages, PG_private should be set with 1 extra refcount,
+ * which is used for page reclaim / migration.
*/
-#define Z_EROFS_MAPPING_STAGING ((void *)0x5A110C8D)
-/* check if a page is marked as staging */
-static inline bool z_erofs_page_is_staging(struct page *page)
+/*
+ * short-lived pages are pages directly from buddy system with specific
+ * page->private (no need to set PagePrivate since these are non-LRU /
+ * non-movable pages and bypass reclaim / migration code).
+ */
+static inline bool z_erofs_is_shortlived_page(struct page *page)
{
- return page->mapping == Z_EROFS_MAPPING_STAGING;
+ if (page->private != Z_EROFS_SHORTLIVED_PAGE)
+ return false;
+
+ DBG_BUGON(page->mapping);
+ return true;
}
-static inline bool z_erofs_put_stagingpage(struct list_head *pagepool,
- struct page *page)
+static inline bool z_erofs_put_shortlivedpage(struct list_head *pagepool,
+ struct page *page)
{
- if (!z_erofs_page_is_staging(page))
+ if (!z_erofs_is_shortlived_page(page))
return false;
- /* staging pages should not be used by others at the same time */
- if (page_ref_count(page) > 1)
+ /* short-lived pages should not be used by others at the same time */
+ if (page_ref_count(page) > 1) {
put_page(page);
- else
+ } else {
+ /* follow the pcluster rule above. */
+ set_page_private(page, 0);
list_add(&page->lru, pagepool);
+ }
return true;
}
diff --git a/fs/erofs/decompressor.c b/fs/erofs/decompressor.c
index cbadbf55c6c2..1cb1ffd10569 100644
--- a/fs/erofs/decompressor.c
+++ b/fs/erofs/decompressor.c
@@ -76,7 +76,7 @@ static int z_erofs_lz4_prepare_destpages(struct z_erofs_decompress_req *rq,
victim = erofs_allocpage(pagepool, GFP_KERNEL);
if (!victim)
return -ENOMEM;
- victim->mapping = Z_EROFS_MAPPING_STAGING;
+ set_page_private(victim, Z_EROFS_SHORTLIVED_PAGE);
}
rq->out[i] = victim;
}
diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
index 86fd3bf62af6..cfb0d11f893b 100644
--- a/fs/erofs/zdata.c
+++ b/fs/erofs/zdata.c
@@ -226,11 +226,8 @@ int erofs_try_to_free_all_cached_pages(struct erofs_sb_info *sbi,
/* barrier is implied in the following 'unlock_page' */
WRITE_ONCE(pcl->compressed_pages[i], NULL);
- set_page_private(page, 0);
- ClearPagePrivate(page);
-
+ detach_page_private(page);
unlock_page(page);
- put_page(page);
}
return 0;
}
@@ -254,10 +251,8 @@ int erofs_try_to_free_cached_page(struct address_space *mapping,
}
erofs_workgroup_unfreeze(&pcl->obj, 1);
- if (ret) {
- ClearPagePrivate(page);
- put_page(page);
- }
+ if (ret)
+ detach_page_private(page);
}
return ret;
}
@@ -648,12 +643,12 @@ static int z_erofs_do_read_page(struct z_erofs_decompress_frontend *fe,
retry:
err = z_erofs_attach_page(clt, page, page_type);
- /* should allocate an additional staging page for pagevec */
+ /* should allocate an additional short-lived page for pagevec */
if (err == -EAGAIN) {
struct page *const newpage =
alloc_page(GFP_NOFS | __GFP_NOFAIL);
- newpage->mapping = Z_EROFS_MAPPING_STAGING;
+ set_page_private(newpage, Z_EROFS_SHORTLIVED_PAGE);
err = z_erofs_attach_page(clt, newpage,
Z_EROFS_PAGE_TYPE_EXCLUSIVE);
if (!err)
@@ -710,6 +705,11 @@ static void z_erofs_decompress_kickoff(struct z_erofs_decompressqueue *io,
queue_work(z_erofs_workqueue, &io->u.work);
}
+static bool z_erofs_page_is_invalidated(struct page *page)
+{
+ return !page->mapping && !z_erofs_is_shortlived_page(page);
+}
+
static void z_erofs_decompressqueue_endio(struct bio *bio)
{
tagptr1_t t = tagptr_init(tagptr1_t, bio->bi_private);
@@ -722,7 +722,7 @@ static void z_erofs_decompressqueue_endio(struct bio *bio)
struct page *page = bvec->bv_page;
DBG_BUGON(PageUptodate(page));
- DBG_BUGON(!page->mapping);
+ DBG_BUGON(z_erofs_page_is_invalidated(page));
if (err)
SetPageError(page);
@@ -795,9 +795,9 @@ static int z_erofs_decompress_pcluster(struct super_block *sb,
/* all pages in pagevec ought to be valid */
DBG_BUGON(!page);
- DBG_BUGON(!page->mapping);
+ DBG_BUGON(z_erofs_page_is_invalidated(page));
- if (z_erofs_put_stagingpage(pagepool, page))
+ if (z_erofs_put_shortlivedpage(pagepool, page))
continue;
if (page_type == Z_EROFS_VLE_PAGE_TYPE_HEAD)
@@ -831,9 +831,9 @@ static int z_erofs_decompress_pcluster(struct super_block *sb,
/* all compressed pages ought to be valid */
DBG_BUGON(!page);
- DBG_BUGON(!page->mapping);
+ DBG_BUGON(z_erofs_page_is_invalidated(page));
- if (!z_erofs_page_is_staging(page)) {
+ if (!z_erofs_is_shortlived_page(page)) {
if (erofs_page_is_managed(sbi, page)) {
if (!PageUptodate(page))
err = -EIO;
@@ -858,7 +858,7 @@ static int z_erofs_decompress_pcluster(struct super_block *sb,
overlapped = true;
}
- /* PG_error needs checking for inplaced and staging pages */
+ /* PG_error needs checking for all non-managed pages */
if (PageError(page)) {
DBG_BUGON(PageUptodate(page));
err = -EIO;
@@ -897,8 +897,8 @@ static int z_erofs_decompress_pcluster(struct super_block *sb,
if (erofs_page_is_managed(sbi, page))
continue;
- /* recycle all individual staging pages */
- (void)z_erofs_put_stagingpage(pagepool, page);
+ /* recycle all individual short-lived pages */
+ (void)z_erofs_put_shortlivedpage(pagepool, page);
WRITE_ONCE(compressed_pages[i], NULL);
}
@@ -908,10 +908,10 @@ static int z_erofs_decompress_pcluster(struct super_block *sb,
if (!page)
continue;
- DBG_BUGON(!page->mapping);
+ DBG_BUGON(z_erofs_page_is_invalidated(page));
- /* recycle all individual staging pages */
- if (z_erofs_put_stagingpage(pagepool, page))
+ /* recycle all individual short-lived pages */
+ if (z_erofs_put_shortlivedpage(pagepool, page))
continue;
if (err < 0)
@@ -1011,13 +1011,17 @@ static struct page *pickup_page_for_submission(struct z_erofs_pcluster *pcl,
mapping = READ_ONCE(page->mapping);
/*
- * unmanaged (file) pages are all locked solidly,
+ * file-backed online pages in plcuster are all locked steady,
* therefore it is impossible for `mapping' to be NULL.
*/
if (mapping && mapping != mc)
/* ought to be unmanaged pages */
goto out;
+ /* directly return for shortlived page as well */
+ if (z_erofs_is_shortlived_page(page))
+ goto out;
+
lock_page(page);
/* only true if page reclaim goes wrong, should never happen */
@@ -1062,8 +1066,8 @@ static struct page *pickup_page_for_submission(struct z_erofs_pcluster *pcl,
out_allocpage:
page = erofs_allocpage(pagepool, gfp | __GFP_NOFAIL);
if (!tocache || add_to_page_cache_lru(page, mc, index + nr, gfp)) {
- /* non-LRU / non-movable temporary page is needed */
- page->mapping = Z_EROFS_MAPPING_STAGING;
+ /* turn into temporary page if fails */
+ set_page_private(page, Z_EROFS_SHORTLIVED_PAGE);
tocache = false;
}
@@ -1080,8 +1084,9 @@ static struct page *pickup_page_for_submission(struct z_erofs_pcluster *pcl,
}
if (tocache) {
- set_page_private(page, (unsigned long)pcl);
- SetPagePrivate(page);
+ attach_page_private(page, pcl);
+ /* drop a ref added by allocpage (then we have 2 refs here) */
+ put_page(page);
}
out: /* the only exit (for tracing and debugging) */
return page;
diff --git a/fs/erofs/zdata.h b/fs/erofs/zdata.h
index 68c9b29fc0ca..b503b353d4ab 100644
--- a/fs/erofs/zdata.h
+++ b/fs/erofs/zdata.h
@@ -173,6 +173,7 @@ static inline void z_erofs_onlinepage_endio(struct page *page)
v = atomic_dec_return(u.o);
if (!(v & Z_EROFS_ONLINEPAGE_COUNT_MASK)) {
+ set_page_private(page, 0);
ClearPagePrivate(page);
if (!PageError(page))
SetPageUptodate(page);
--
2.18.4