From: "Matthew Wilcox (Oracle)" <[email protected]>
Eliminate the page_offset variable which was just confusing;
record the start of each consecutive run of pages in the
readahead_control, and move the 'kick off a fresh batch' code to
the end of the function for easier use in the next patch.
Signed-off-by: Matthew Wilcox (Oracle) <[email protected]>
---
mm/readahead.c | 31 +++++++++++++++++++------------
1 file changed, 19 insertions(+), 12 deletions(-)
diff --git a/mm/readahead.c b/mm/readahead.c
index 15329309231f..74791b96013f 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -154,7 +154,6 @@ void __do_page_cache_readahead(struct address_space *mapping,
unsigned long lookahead_size)
{
struct inode *inode = mapping->host;
- struct page *page;
unsigned long end_index; /* The last page we want to read */
LIST_HEAD(page_pool);
int page_idx;
@@ -163,6 +162,7 @@ void __do_page_cache_readahead(struct address_space *mapping,
struct readahead_control rac = {
.mapping = mapping,
.file = filp,
+ ._start = offset,
._nr_pages = 0,
};
@@ -175,32 +175,39 @@ void __do_page_cache_readahead(struct address_space *mapping,
* Preallocate as many pages as we will need.
*/
for (page_idx = 0; page_idx < nr_to_read; page_idx++) {
- pgoff_t page_offset = offset + page_idx;
+ struct page *page;
- if (page_offset > end_index)
+ if (offset > end_index)
break;
- page = xa_load(&mapping->i_pages, page_offset);
+ page = xa_load(&mapping->i_pages, offset);
if (page && !xa_is_value(page)) {
/*
- * Page already present? Kick off the current batch of
- * contiguous pages before continuing with the next
- * batch.
+ * Page already present? Kick off the current batch
+ * of contiguous pages before continuing with the
+ * next batch. This page may be the one we would
+ * have intended to mark as Readahead, but we don't
+ * have a stable reference to this page, and it's
+ * not worth getting one just for that.
*/
- if (readahead_count(&rac))
- read_pages(&rac, &page_pool, gfp_mask);
- rac._nr_pages = 0;
- continue;
+ goto read;
}
page = __page_cache_alloc(gfp_mask);
if (!page)
break;
- page->index = page_offset;
+ page->index = offset;
list_add(&page->lru, &page_pool);
if (page_idx == nr_to_read - lookahead_size)
SetPageReadahead(page);
rac._nr_pages++;
+ offset++;
+ continue;
+read:
+ if (readahead_count(&rac))
+ read_pages(&rac, &page_pool, gfp_mask);
+ rac._nr_pages = 0;
+ rac._start = ++offset;
}
/*
--
2.25.0
On 2/17/20 10:45 AM, Matthew Wilcox wrote:
> From: "Matthew Wilcox (Oracle)" <[email protected]>
>
> Eliminate the page_offset variable which was just confusing;
> record the start of each consecutive run of pages in the
OK...presumably for the benefit of a following patch, since it is not
actually consumed in this patch.
> readahead_control, and move the 'kick off a fresh batch' code to
> the end of the function for easier use in the next patch.
That last bit was actually done in the previous patch, rather than this
one, right?
>
> Signed-off-by: Matthew Wilcox (Oracle) <[email protected]>
> ---
> mm/readahead.c | 31 +++++++++++++++++++------------
> 1 file changed, 19 insertions(+), 12 deletions(-)
>
> diff --git a/mm/readahead.c b/mm/readahead.c
> index 15329309231f..74791b96013f 100644
> --- a/mm/readahead.c
> +++ b/mm/readahead.c
> @@ -154,7 +154,6 @@ void __do_page_cache_readahead(struct address_space *mapping,
> unsigned long lookahead_size)
> {
> struct inode *inode = mapping->host;
> - struct page *page;
> unsigned long end_index; /* The last page we want to read */
> LIST_HEAD(page_pool);
> int page_idx;
> @@ -163,6 +162,7 @@ void __do_page_cache_readahead(struct address_space *mapping,
> struct readahead_control rac = {
> .mapping = mapping,
> .file = filp,
> + ._start = offset,
> ._nr_pages = 0,
> };
>
> @@ -175,32 +175,39 @@ void __do_page_cache_readahead(struct address_space *mapping,
> * Preallocate as many pages as we will need.
> */
> for (page_idx = 0; page_idx < nr_to_read; page_idx++) {
> - pgoff_t page_offset = offset + page_idx;
You know...this ends up incrementing offset each time through the
loop, so yes, the behavior is the same as when using "offset + page_idx".
However, now it's a little harder to see that.
IMHO the page_offset variable is not actually a bad thing, here. I'd rather
keep it, all other things being equal (and I don't see any other benefits
here: line count is the same, for example).
What do you think?
thanks,
--
John Hubbard
NVIDIA
> + struct page *page;
>
> - if (page_offset > end_index)
> + if (offset > end_index)
> break;
>
> - page = xa_load(&mapping->i_pages, page_offset);
> + page = xa_load(&mapping->i_pages, offset);
> if (page && !xa_is_value(page)) {
> /*
> - * Page already present? Kick off the current batch of
> - * contiguous pages before continuing with the next
> - * batch.
> + * Page already present? Kick off the current batch
> + * of contiguous pages before continuing with the
> + * next batch. This page may be the one we would
> + * have intended to mark as Readahead, but we don't
> + * have a stable reference to this page, and it's
> + * not worth getting one just for that.
> */
> - if (readahead_count(&rac))
> - read_pages(&rac, &page_pool, gfp_mask);
> - rac._nr_pages = 0;
> - continue;
> + goto read;
> }
>
> page = __page_cache_alloc(gfp_mask);
> if (!page)
> break;
> - page->index = page_offset;
> + page->index = offset;
> list_add(&page->lru, &page_pool);
> if (page_idx == nr_to_read - lookahead_size)
> SetPageReadahead(page);
> rac._nr_pages++;
> + offset++;
> + continue;
> +read:
> + if (readahead_count(&rac))
> + read_pages(&rac, &page_pool, gfp_mask);
> + rac._nr_pages = 0;
> + rac._start = ++offset;
> }
>
> /*
>
On 2/18/20 2:57 PM, John Hubbard wrote:
> On 2/17/20 10:45 AM, Matthew Wilcox wrote:
>> From: "Matthew Wilcox (Oracle)" <[email protected]>
>>
>> Eliminate the page_offset variable which was just confusing;
>> record the start of each consecutive run of pages in the
>
>
Darn it, I incorrectly reviewed the N/16 patch, instead of the N/19, for
this one. I thought I had deleted all those! Let me try again with the
correct patch, sorry!!
thanks,
--
John Hubbard
NVIDIA
> OK...presumably for the benefit of a following patch, since it is not
> actually consumed in this patch.
>
>> readahead_control, and move the 'kick off a fresh batch' code to
>> the end of the function for easier use in the next patch.
>
>
> That last bit was actually done in the previous patch, rather than this
> one, right?
>
>>
>> Signed-off-by: Matthew Wilcox (Oracle) <[email protected]>
>> ---
>> mm/readahead.c | 31 +++++++++++++++++++------------
>> 1 file changed, 19 insertions(+), 12 deletions(-)
>>
>> diff --git a/mm/readahead.c b/mm/readahead.c
>> index 15329309231f..74791b96013f 100644
>> --- a/mm/readahead.c
>> +++ b/mm/readahead.c
>> @@ -154,7 +154,6 @@ void __do_page_cache_readahead(struct address_space *mapping,
>> unsigned long lookahead_size)
>> {
>> struct inode *inode = mapping->host;
>> - struct page *page;
>> unsigned long end_index; /* The last page we want to read */
>> LIST_HEAD(page_pool);
>> int page_idx;
>> @@ -163,6 +162,7 @@ void __do_page_cache_readahead(struct address_space *mapping,
>> struct readahead_control rac = {
>> .mapping = mapping,
>> .file = filp,
>> + ._start = offset,
>> ._nr_pages = 0,
>> };
>>
>> @@ -175,32 +175,39 @@ void __do_page_cache_readahead(struct address_space *mapping,
>> * Preallocate as many pages as we will need.
>> */
>> for (page_idx = 0; page_idx < nr_to_read; page_idx++) {
>> - pgoff_t page_offset = offset + page_idx;
>
>
> You know...this ends up incrementing offset each time through the
> loop, so yes, the behavior is the same as when using "offset + page_idx".
> However, now it's a little harder to see that.
>
> IMHO the page_offset variable is not actually a bad thing, here. I'd rather
> keep it, all other things being equal (and I don't see any other benefits
> here: line count is the same, for example).
>
> What do you think?
>
>
> thanks,
>