From: Matthew Wilcox <willy@infradead.org>
To: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: linux-mm@kvack.org, linux-fsdevel@vger.kernel.org,
linux-kernel@vger.kernel.org,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Hugh Dickins <hughd@google.com>
Subject: Re: [PATCH 1/2] mm: Remove redundant test from find_get_pages_contig
Date: Fri, 23 Nov 2018 09:59:32 -0800 [thread overview]
Message-ID: <20181123175932.GV3065@bombadil.infradead.org> (raw)
In-Reply-To: <20181123104732.gvhdqyddbsiq3i42@kshutemo-mobl1>
On Fri, Nov 23, 2018 at 01:47:32PM +0300, Kirill A. Shutemov wrote:
> On Thu, Nov 22, 2018 at 01:32:23PM -0800, Matthew Wilcox wrote:
> > After we establish a reference on the page, we check the pointer continues
> > to be in the correct position in i_pages. There's no need to check the
> > page->mapping or page->index afterwards; if those can change after we've
> > got the reference, they can change after we return the page to the caller.
>
> Hm. IIRC, page->mapping can be set to NULL due truncation, but what about
> index? When it can be changed? Truncation doesn't touch it.
I think index can only be changed after the refcount has hit zero and
the page is safely out of the pagecache. I agree that page->mapping can
be set to NULL after the call to xas_reload() ... but then it can also
happen after the check, so the check isn't really buying us anything
that the xas_reload() call doesn't already check.
next prev parent reply other threads:[~2018-11-23 17:59 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-22 21:32 [PATCH 0/2] Better support for THP in page cache Matthew Wilcox
2018-11-22 21:32 ` [PATCH 1/2] mm: Remove redundant test from find_get_pages_contig Matthew Wilcox
2018-11-23 10:47 ` Kirill A. Shutemov
2018-11-23 17:59 ` Matthew Wilcox [this message]
2018-11-22 21:32 ` [PATCH 2/2] page cache: Store only head pages in i_pages Matthew Wilcox
2018-11-23 10:56 ` Kirill A. Shutemov
2018-11-23 17:19 ` Matthew Wilcox
2018-11-23 17:36 ` Kirill A. Shutemov
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