We need to call extent_range_clear_dirty_for_io()
on compression range to prevent application from changing
page content, while pages compressing.
but "(end - start)" can be much (up to 1024 times) bigger
then compression range (BTRFS_MAX_UNCOMPRESSED), so optimize that
by calculating compression range for
that loop iteration, and flip bits only on that range
v1 -> v2:
- Make that more obviously and more safeprone
v2 -> v3:
- Rebased on:
Btrfs: compress_file_range() remove dead variable num_bytes
- Update change log
- Add comments
Signed-off-by: Timofey Titovets <nefelim4ag@xxxxxxxxx>
---
fs/btrfs/inode.c | 27 ++++++++++++++++++++++-----
1 file changed, 22 insertions(+), 5 deletions(-)
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 237df8fdf7b8..b6e81bd650ea 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -460,6 +460,7 @@ static noinline void compress_file_range(struct inode *inode,
struct btrfs_root *root = BTRFS_I(inode)->root;
u64 blocksize = fs_info->sectorsize;
u64 actual_end;
+ u64 current_end;
u64 isize = i_size_read(inode);
int ret = 0;
struct page **pages = NULL;
@@ -505,6 +506,21 @@ static noinline void compress_file_range(struct inode *inode,
(start > 0 || end + 1 < BTRFS_I(inode)->disk_i_size))
goto cleanup_and_bail_uncompressed;
+ /*
+ * We need to call extent_range_clear_dirty_for_io()
+ * on compression range to prevent application from changing
+ * page content, while pages compressing.
+ *
+ * but (end - start) can be much (up to 1024 times) bigger
+ * then compression range, so optimize that
+ * by calculating compression range for
+ * that iteration, and flip bits only on that range
+ */
+ if (end - start > BTRFS_MAX_UNCOMPRESSED)
+ current_end = start + BTRFS_MAX_UNCOMPRESSED;
+ else
+ current_end = end;
+
total_compressed = min_t(unsigned long, total_compressed,
BTRFS_MAX_UNCOMPRESSED);
total_in = 0;
@@ -515,7 +531,7 @@ static noinline void compress_file_range(struct inode *inode,
* inode has not been flagged as nocompress. This flag can
* change at any time if we discover bad compression ratios.
*/
- if (inode_need_compress(inode, start, end)) {
+ if (inode_need_compress(inode, start, current_end)) {
WARN_ON(pages);
pages = kcalloc(nr_pages, sizeof(struct page *), GFP_NOFS);
if (!pages) {
@@ -530,14 +546,15 @@ static noinline void compress_file_range(struct inode *inode,
/*
* we need to call clear_page_dirty_for_io on each
- * page in the range. Otherwise applications with the file
- * mmap'd can wander in and change the page contents while
+ * page in compression the range.
+ * Otherwise applications with the file mmap'd
+ * can wander in and change the page contents while
* we are compressing them.
*
* If the compression fails for any reason, we set the pages
* dirty again later on.
*/
- extent_range_clear_dirty_for_io(inode, start, end);
+ extent_range_clear_dirty_for_io(inode, start, current_end);
redirty = 1;
/* Compression level is applied here and only here */
@@ -678,7 +695,7 @@ static noinline void compress_file_range(struct inode *inode,
/* unlocked later on in the async handlers */
if (redirty)
- extent_range_redirty_for_io(inode, start, end);
+ extent_range_redirty_for_io(inode, start, current_end);
add_async_extent(async_cow, start, end - start + 1, 0, NULL, 0,
BTRFS_COMPRESS_NONE);
*num_added += 1;
--
2.14.2
--
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