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charset=us-ascii Content-Disposition: inline In-Reply-To: <20200211035412.GR8731@bombadil.infradead.org> User-Agent: Mutt/1.10.1 (2018-07-13) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, Feb 10, 2020 at 07:54:12PM -0800, Matthew Wilcox wrote: > 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. Sorry about being not clear. I am saying filemap_fault -> do_async_mmap_readahead Let's assume the page is hit in page cache and vmf->flags is !FAULT_FLAG TRIED so it calls do_async_mmap_readahead. Since the page has PG_reclaim and PG_writeback by shrink_page_list, it goes to do_async_mmap_readahead if (PageReadahead(page)) fpin = maybe_unlock_mmap_for_io(); page_cache_async_readahead if (PageWriteback(page)) return; ClearPageReadahead(page); <- doesn't reach here until the writeback is clear So, mm_populate will repeat the loop until the writeback is done. It's my just theory but didn't comfirm it by the testing. If I miss something clear, let me know it. Thanks! > > > > > > > /* > > > * Same bit is used for PG_readahead and PG_reclaim. > > > */ > > > if (PageWriteback(page)) > > > return; > > > > > > ClearPageReadahead(page);