linux-kernel - Re: [PATCH] mm/filemap: Drop check for truncated page after I/O

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Message-ID: <4BF4F395-B102-4FAE-9AD9-9EDE93F5E6FB@oracle.com>
Date:   Thu, 4 Mar 2021 22:50:45 +0000
From:   William Kucharski <william.kucharski@...cle.com>
To:     "Matthew Wilcox (Oracle)" <willy@...radead.org>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Miklos Szeredi <mszeredi@...hat.com>
Subject: Re: [PATCH] mm/filemap: Drop check for truncated page after I/O

LGTM.

Reviewed-by: William Kucharski <william.kucharski@...cle.com>

> On Mar 3, 2021, at 3:25 PM, Matthew Wilcox (Oracle) <willy@...radead.org> wrote:
> 
> If the I/O completed successfully, the page will remain Uptodate,
> even if it is subsequently truncated.  If the I/O completed with an error,
> this check would cause us to retry the I/O if the page were truncated
> before we woke up.  There is no need to retry the I/O; the I/O to fill
> the page failed, so we can legitimately just return -EIO.
> 
> This code was originally added by commit 56f0d5fe6851 ("[PATCH]
> readpage-vs-invalidate fix") in 2005 (this commit ID is from the
> linux-fullhistory tree; it is also commit ba1f08f14b52 in tglx-history).
> 
> At the time, truncate_complete_page() called ClearPageUptodate(), and
> so this was fixing a real bug.  In 2008, commit 84209e02de48
> ("mm: dont clear PG_uptodate on truncate/invalidate") removed the
> call to ClearPageUptodate, and this check has been unnecessary ever
> since.
> 
> It doesn't do any real harm, but there's no need to keep it.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> ---
> mm/filemap.c | 2 --
> 1 file changed, 2 deletions(-)
> 
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 8d3e0daed7c9..3d1635d3be3e 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -2238,8 +2238,6 @@ static int filemap_read_page(struct file *file, struct address_space *mapping,
> 		return error;
> 	if (PageUptodate(page))
> 		return 0;
> -	if (!page->mapping)	/* page truncated */
> -		return AOP_TRUNCATED_PAGE;
> 	shrink_readahead_size_eio(&file->f_ra);
> 	return -EIO;
> }
> -- 
> 2.30.0
> 
>