From: Andrew Morton <email@example.com> To: Matthew Wilcox <firstname.lastname@example.org> Cc: email@example.com, firstname.lastname@example.org, Kent Overstreet <email@example.com>, Christoph Hellwig <firstname.lastname@example.org> Subject: Re: [PATCH] mm/filemap: Use filemap_read_page in filemap_fault Date: Wed, 3 Mar 2021 13:51:42 -0800 [thread overview] Message-ID: <email@example.com> (raw) In-Reply-To: <20210303205736.GG2723601@casper.infradead.org> On Wed, 3 Mar 2021 20:57:36 +0000 Matthew Wilcox <firstname.lastname@example.org> wrote: > On Wed, Mar 03, 2021 at 12:12:53PM -0800, Andrew Morton wrote: > > On Wed, 3 Mar 2021 13:26:40 +0000 Matthew Wilcox <email@example.com> wrote: > > > > > But here's the thing ... invalidate_mapping_pages() doesn't > > > ClearPageUptodate. The only places where we ClearPageUptodate is on an > > > I/O error. > > > > yup. > > > > > So ... as far as I can tell, the only way to hit this is: > > > > > > - Get an I/O error during the wait > > > - Have another thread cause the page to be removed from the page cache > > > (eg do direct I/O to the file) before this thread is run. > > > > > > and the consequence to this change is that we have another attempt to > > > read the page instead of returning an error immediately. I'm OK with > > > that unintentional change, although I think the previous behaviour was > > > also perfectly acceptable (after all, there was an I/O error while trying > > > to read this page). > > > > > > Delving into the linux-fullhistory tree, this code was introduced by ... > > > > > > commit 56f0d5fe6851037214a041a5cb4fc66199256544 > > > Author: Andrew Morton <firstname.lastname@example.org> > > > Date: Fri Jan 7 22:03:01 2005 -0800 > > > > > > [PATCH] readpage-vs-invalidate fix > > > > > > A while ago we merged a patch which tried to solve a problem wherein a > > > concurrent read() and invalidate_inode_pages() would cause the read() to > > > return -EIO because invalidate cleared PageUptodate() at the wrong time. > > > > > > We no longer clear PageUptodate, so I think this is stale code? Perhaps > > > you could check with the original author ... > > > > Which code do you think might be stale? We need the !PageUptodate > > check to catch IO errors and we need the !page->mapping check to catch > > invalidates. Am a bit confused. > > I think the check of !page->mapping here: > > if (PageUptodate(page)) > return 0; > if (!page->mapping) /* page truncated */ > return AOP_TRUNCATED_PAGE; > > is no longer needed. If we didn't see an error, the page will be Uptodate, > regardless of whether it's been removed from the page cache. If we did > see an error, it's OK to return -EIO, even if the page has been removed > from the page cache in the interim. OK. Checking page->mapping of an unlocked page seems meaningless anyway - what's to prevent it from being truncated just after we checked?
next prev parent reply other threads:[~2021-03-04 0:21 UTC|newest] Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-02-26 14:00 Matthew Wilcox (Oracle) 2021-03-03 1:30 ` Andrew Morton 2021-03-03 1:33 ` Matthew Wilcox 2021-03-03 6:07 ` Andrew Morton 2021-03-03 13:26 ` Matthew Wilcox 2021-03-03 20:12 ` Andrew Morton 2021-03-03 20:57 ` Matthew Wilcox 2021-03-03 21:51 ` Andrew Morton [this message] 2021-03-03 22:31 ` Matthew Wilcox
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