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btrfs: improve the delalloc_to_write calculation in writepage_delalloc

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Currently writepage_delalloc adds to delalloc_to_write in every loop
operation.  That is not only more work than doing it once after the
loop, but can also over-increment the counter due to rounding errors
when a new loop iteration starts with an offset into a page.

Add a new page_start variable instead of recaculation that value over
and over, move the delalloc_to_write calculation out of the loop, use
the DIV_ROUND_UP helper instead of open coding it and remove the pointless
found local variable.

Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Christoph Hellwig
2023-06-28 17:31:30 +02:00
committed by David Sterba
parent 0835d1e66e
commit 2c73162d64
1 changed files with 14 additions and 15 deletions
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29
fs/btrfs/extent_io.c
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@@ -1185,8 +1185,10 @@ static inline void contiguous_readpages(struct page *pages[], int nr_pages,
static noinline_for_stack int writepage_delalloc(struct btrfs_inode *inode,
struct page *page, struct writeback_control *wbc)
{
const u64 page_end = page_offset(page) + PAGE_SIZE - 1;
u64 delalloc_start = page_offset(page);
const u64 page_start = page_offset(page);
const u64 page_end = page_start + PAGE_SIZE - 1;
u64 delalloc_start = page_start;
u64 delalloc_end = page_end;
u64 delalloc_to_write = 0;
/* How many pages are started by btrfs_run_delalloc_range() */
unsigned long nr_written = 0;
@@ -1194,13 +1196,9 @@ static noinline_for_stack int writepage_delalloc(struct btrfs_inode *inode,
int page_started = 0;
while (delalloc_start < page_end) {
u64 delalloc_end = page_end;
bool found;
found = find_lock_delalloc_range(&inode->vfs_inode, page,
&delalloc_start,
&delalloc_end);
if (!found) {
delalloc_end = page_end;
if (!find_lock_delalloc_range(&inode->vfs_inode, page,
&delalloc_start, &delalloc_end)) {
delalloc_start = delalloc_end + 1;
continue;
}
@@ -1209,14 +1207,15 @@ static noinline_for_stack int writepage_delalloc(struct btrfs_inode *inode,
if (ret)
return ret;
/*
* delalloc_end is already one less than the total length, so
* we don't subtract one from PAGE_SIZE
*/
delalloc_to_write += (delalloc_end - delalloc_start +
PAGE_SIZE) >> PAGE_SHIFT;
delalloc_start = delalloc_end + 1;
}
/*
* delalloc_end is already one less than the total length, so
* we don't subtract one from PAGE_SIZE
*/
delalloc_to_write +=
DIV_ROUND_UP(delalloc_end + 1 - page_start, PAGE_SIZE);
if (wbc->nr_to_write < delalloc_to_write) {
int thresh = 8192;