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SubjectRe: [PATCH] mm: change may_enter_fs check condition
On Fri 13-11-15 13:01:16, Vlastimil Babka wrote:
> On 11/13/2015 12:47 PM, yalin wang wrote:
> >Add page_is_file_cache() for __GFP_FS check,
> >otherwise, a Pageswapcache() && PageDirty() page can always be write
> >back if the gfp flag is __GFP_FS, this is not the expected behavior.
>
> I'm not sure I understand your point correctly *), but you seem to imply
> that there would be an allocation that has __GFP_FS but doesn't have
> __GFP_IO? Are there such allocations and does it make sense?

No it doesn't. There is a natural layering here and __GFP_FS allocations
should contain __GFP_IO.

The patch as is makes only little sense to me. Are you seeing any issue
which this is trying to fix?

> *) It helps to state which problem you actually observed and are trying to
> fix. Or was this found by code inspection? In that case describe the
> theoretical problem, as "expected behavior" isn't always understood by
> everyone the same.
>
> >Signed-off-by: yalin wang <yalin.wang2010@gmail.com>
> >---
> > mm/vmscan.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> >diff --git a/mm/vmscan.c b/mm/vmscan.c
> >index bd2918e..f8fc8c1 100644
> >--- a/mm/vmscan.c
> >+++ b/mm/vmscan.c
> >@@ -930,7 +930,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
> > if (page_mapped(page) || PageSwapCache(page))
> > sc->nr_scanned++;
> >
> >- may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
> >+ may_enter_fs = (page_is_file_cache(page) && (sc->gfp_mask & __GFP_FS)) ||
> > (PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));
> >
> > /*
> >

--
Michal Hocko
SUSE Labs


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