Subject: [PATCH v2] mm/page-writeback.c: write_cache_pages(): deduplicate identical checks

There used to be a 'retry' label in between the two (identical) checks
when first introduced in commit f446daaea9d4 ("mm: implement writeback
livelock avoidance using page tagging"), and later modified/updated in
commit 6e6938b6d313 ("writeback: introduce .tagged_writepages for the
WB_SYNC_NONE sync stage").

The label has been removed in commit 64081362e8ff ("mm/page-writeback.c:
fix range_cyclic writeback vs writepages deadlock"), and the (identical)
checks are now present / performed immediately one after another.

So, remove/deduplicate the latter check, moving tag_pages_for_writeback()
into the former check before the 'tag' variable assignment, so it's clear
that it's not used in this (similarly-named) function call but only later
in pagevec_lookup_range_tag().

Signed-off-by: Mauricio Faria de Oliveira <[email protected]>
---

v2: add the missing braces to the conditional statement
with more than a single statement.. doh; and to the
else branch (w/a single statement, per coding style.)

mm/page-writeback.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 2caf780a42e7..ab5a3cee8ad3 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2182,12 +2182,12 @@ int write_cache_pages(struct address_space *mapping,
if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
range_whole = 1;
}
- if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
+ if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages) {
+ tag_pages_for_writeback(mapping, index, end);
tag = PAGECACHE_TAG_TOWRITE;
- else
+ } else {
tag = PAGECACHE_TAG_DIRTY;
- if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
- tag_pages_for_writeback(mapping, index, end);
+ }
done_index = index;
while (!done && (index <= end)) {
int i;
--
2.20.1


2020-02-19 00:21:12

by Ira Weiny

[permalink] [raw]
Subject: Re: [PATCH v2] mm/page-writeback.c: write_cache_pages(): deduplicate identical checks

On Tue, Feb 18, 2020 at 07:17:16PM -0300, Mauricio Faria de Oliveira wrote:
> There used to be a 'retry' label in between the two (identical) checks
> when first introduced in commit f446daaea9d4 ("mm: implement writeback
> livelock avoidance using page tagging"), and later modified/updated in
> commit 6e6938b6d313 ("writeback: introduce .tagged_writepages for the
> WB_SYNC_NONE sync stage").
>
> The label has been removed in commit 64081362e8ff ("mm/page-writeback.c:
> fix range_cyclic writeback vs writepages deadlock"), and the (identical)
> checks are now present / performed immediately one after another.
>
> So, remove/deduplicate the latter check, moving tag_pages_for_writeback()
> into the former check before the 'tag' variable assignment, so it's clear
> that it's not used in this (similarly-named) function call but only later
> in pagevec_lookup_range_tag().
>
> Signed-off-by: Mauricio Faria de Oliveira <[email protected]>

Reviewed-by: Ira Weiny <[email protected]>

> ---
>
> v2: add the missing braces to the conditional statement
> with more than a single statement.. doh; and to the
> else branch (w/a single statement, per coding style.)
>
> mm/page-writeback.c | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index 2caf780a42e7..ab5a3cee8ad3 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -2182,12 +2182,12 @@ int write_cache_pages(struct address_space *mapping,
> if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
> range_whole = 1;
> }
> - if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
> + if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages) {
> + tag_pages_for_writeback(mapping, index, end);
> tag = PAGECACHE_TAG_TOWRITE;
> - else
> + } else {
> tag = PAGECACHE_TAG_DIRTY;
> - if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
> - tag_pages_for_writeback(mapping, index, end);
> + }
> done_index = index;
> while (!done && (index <= end)) {
> int i;
> --
> 2.20.1
>