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SubjectRe: [PATCH] mm: fix long time stall from mm_populate
On Mon, Feb 10, 2020 at 07:50:04PM -0800, Minchan Kim wrote:
> On Mon, Feb 10, 2020 at 05:10:21PM -0800, Matthew Wilcox wrote:
> > On Mon, Feb 10, 2020 at 04:19:58PM -0800, Minchan Kim wrote:
> > > filemap_fault
> > > find a page form page(PG_uptodate|PG_readahead|PG_writeback)
> >
> > Uh ... That shouldn't be possible.
>
> Please see shrink_page_list. Vmscan uses PG_reclaim to accelerate
> page reclaim when the writeback is done so the page will have both
> flags at the same time and the PG reclaim could be regarded as
> PG_readahead in fault conext.

What part of fault context can make that mistake? The snippet I quoted
below is from page_cache_async_readahead() where it will clearly not
make that mistake. There's a lot of code here; please don't presume I
know all the areas you're talking about.

> >
> > /*
> > * Same bit is used for PG_readahead and PG_reclaim.
> > */
> > if (PageWriteback(page))
> > return;
> >
> > ClearPageReadahead(page);

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