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SubjectRe: [f2fs-dev] [PATCH] f2fs: fix retry logic in f2fs_write_cache_pages()
On 05/28, Chao Yu wrote:
> On 2020/5/28 10:45, Chao Yu wrote:
> > On 2020/5/27 10:20, Sahitya Tummala wrote:
> >> In case a compressed file is getting overwritten, the current retry
> >> logic doesn't include the current page to be retried now as it sets
> >> the new start index as 0 and new end index as writeback_index - 1.
> >> This causes the corresponding cluster to be uncompressed and written
> >> as normal pages without compression. Fix this by allowing writeback to
> >> be retried for the current page as well (in case of compressed page
> >> getting retried due to index mismatch with cluster index). So that
> >> this cluster can be written compressed in case of overwrite.
> >>
> >> Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
> >> ---
> >> fs/f2fs/data.c | 2 +-
> >> 1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> >> index 4af5fcd..bfd1df4 100644
> >> --- a/fs/f2fs/data.c
> >> +++ b/fs/f2fs/data.c
> >> @@ -3024,7 +3024,7 @@ static int f2fs_write_cache_pages(struct address_space *mapping,
> >> if ((!cycled && !done) || retry) {
> >
> > IMO, we add retry logic in wrong place, you can see that cycled value is
> > zero only if wbc->range_cyclic is true, in that case writeback_index is valid.
> >
> > However if retry is true and wbc->range_cyclic is false, then writeback_index
> > would be uninitialized variable.
> >
> > Thoughts?
> >
> > Thanks,
> >
> >> cycled = 1;
> >> index = 0;
> >> - end = writeback_index - 1;
>
> BTW, I notice that range_cyclic writeback flow was refactored in below commit,
> and skeleton of f2fs.writepages was copied from mm/page-writeback.c::write_cache_pages(),
> I guess we need follow that change.
>
> 64081362e8ff ("mm/page-writeback.c: fix range_cyclic writeback vs writepages deadlock")

Is that something like this?

---
fs/f2fs/data.c | 11 ++---------
1 file changed, 2 insertions(+), 9 deletions(-)

diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 48a622b95b76e..28fcdf0d4dcb9 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -2861,7 +2861,6 @@ static int f2fs_write_cache_pages(struct address_space *mapping,
pgoff_t index;
pgoff_t end; /* Inclusive */
pgoff_t done_index;
- int cycled;
int range_whole = 0;
xa_mark_t tag;
int nwritten = 0;
@@ -2879,17 +2878,12 @@ static int f2fs_write_cache_pages(struct address_space *mapping,
if (wbc->range_cyclic) {
writeback_index = mapping->writeback_index; /* prev offset */
index = writeback_index;
- if (index == 0)
- cycled = 1;
- else
- cycled = 0;
end = -1;
} 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;
- cycled = 1; /* ignore range_cyclic tests */
}
if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
tag = PAGECACHE_TAG_TOWRITE;
@@ -3054,10 +3048,9 @@ static int f2fs_write_cache_pages(struct address_space *mapping,
}
}
#endif
- if ((!cycled && !done) || retry) {
- cycled = 1;
+ if (retry) {
index = 0;
- end = writeback_index - 1;
+ end = -1;
goto retry;
}
if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
--
2.27.0.rc0.183.gde8f92d652-goog
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