Re: [PATCH] mm: fix long time stall from mm_populate

[Minchan Kim]

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.

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