linux-kernel - Re: [PATCHv3 0/2] mm: map few pages around fault address if they are in page cache

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Message-ID: <CA+55aFyuspw4viBYbjd=j+zOHe1w-_LMCUHdyTjt4yUqUyosdw@mail.gmail.com>
Date:	Fri, 28 Feb 2014 17:08:22 -0600
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	"Kirill A. Shutemov" <kirill@...temov.name>
Cc:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	Andi Kleen <ak@...ux.intel.com>,
	Matthew Wilcox <matthew.r.wilcox@...el.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Dave Chinner <david@...morbit.com>, Ning Qu <quning@...il.com>,
	linux-mm <linux-mm@...ck.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCHv3 0/2] mm: map few pages around fault address if they are
 in page cache

On Thu, Feb 27, 2014 at 6:10 PM, Kirill A. Shutemov
<kirill@...temov.name> wrote:
>
> Also Matthew noticed that some drivers do ugly hacks like fault in whole
> VMA on first page fault. IIUC, it's for performance reasons. See
> psbfb_vm_fault() or ttm_bo_vm_fault().

I guarantee it's not for performance reasons, it's probably some other breakage.

And if anything really does want to populate things fully, doing so at
fault time is wrong anyway, you should just use MAP_POPULATE at mmap
time.

So I'll believe the shm/tmpfs issue, and that's "mm internal" anyway.
But random crappy drivers? No way in hell.

               Linus
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