From: Mel Gorman <mgorman@suse.de>
To: Christoph Lameter <cl@linux.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Linux-MM <linux-mm@kvack.org>,
Linux-Netdev <netdev@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
David Miller <davem@davemloft.net>, Neil Brown <neilb@suse.de>,
Peter Zijlstra <a.p.zijlstra@chello.nl>
Subject: Re: [PATCH 02/15] mm: sl[au]b: Add knowledge of PFMEMALLOC reserve pages
Date: Wed, 8 Feb 2012 14:45:06 +0000 [thread overview]
Message-ID: <20120208144506.GI5938@suse.de> (raw)
In-Reply-To: <alpine.DEB.2.00.1202071025050.30652@router.home>
On Tue, Feb 07, 2012 at 10:27:56AM -0600, Christoph Lameter wrote:
> On Mon, 6 Feb 2012, Mel Gorman wrote:
>
> > Pages allocated from the reserve are returned with page->pfmemalloc
> > set and it is up to the caller to determine how the page should be
> > protected. SLAB restricts access to any page with page->pfmemalloc set
>
> pfmemalloc sounds like a page flag. If you would use one then the
> preservation of the flag by copying it elsewhere may not be necessary and
> the patches would be less invasive.
Using a page flag would simplify parts of the patch. The catch of course
is that it requires a page flag which are in tight supply and I do not
want to tie this to being 32-bit unnecessarily.
> Also you would not need to extend
> and modify many of the structures.
>
Lets see;
o struct page size would be unaffected
o struct kmem_cache_cpu could be left alone even though it's a small saving
o struct slab also be left alone
o struct array_cache could be left alone although I would point out that
it would make no difference in size as touched is changed to a bool to
fit pfmemalloc in
o It would still be necessary to do the object pointer tricks in slab.c
to avoid doing an excessive number of page lookups which is where much
of the complexity is
o The virt_to_slab could be replaced by looking up the page flag instead
and avoiding a level of indirection that would be pleasing
to an int and placed with struct kmem_cache
I agree that parts of the patch would be simplier although the
complexity of storing pfmemalloc within the obj pointer would probably
remain. However, the downside of requiring a page flag is very high. In
the event we increase the number of page flags - great, I'll use one but
right now I do not think the use of page flag is justified.
--
Mel Gorman
SUSE Labs
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WARNING: multiple messages have this Message-ID (diff)
From: Mel Gorman <mgorman@suse.de>
To: Christoph Lameter <cl@linux.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Linux-MM <linux-mm@kvack.org>,
Linux-Netdev <netdev@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
David Miller <davem@davemloft.net>, Neil Brown <neilb@suse.de>,
Peter Zijlstra <a.p.zijlstra@chello.nl>
Subject: Re: [PATCH 02/15] mm: sl[au]b: Add knowledge of PFMEMALLOC reserve pages
Date: Wed, 8 Feb 2012 14:45:06 +0000 [thread overview]
Message-ID: <20120208144506.GI5938@suse.de> (raw)
In-Reply-To: <alpine.DEB.2.00.1202071025050.30652@router.home>
On Tue, Feb 07, 2012 at 10:27:56AM -0600, Christoph Lameter wrote:
> On Mon, 6 Feb 2012, Mel Gorman wrote:
>
> > Pages allocated from the reserve are returned with page->pfmemalloc
> > set and it is up to the caller to determine how the page should be
> > protected. SLAB restricts access to any page with page->pfmemalloc set
>
> pfmemalloc sounds like a page flag. If you would use one then the
> preservation of the flag by copying it elsewhere may not be necessary and
> the patches would be less invasive.
Using a page flag would simplify parts of the patch. The catch of course
is that it requires a page flag which are in tight supply and I do not
want to tie this to being 32-bit unnecessarily.
> Also you would not need to extend
> and modify many of the structures.
>
Lets see;
o struct page size would be unaffected
o struct kmem_cache_cpu could be left alone even though it's a small saving
o struct slab also be left alone
o struct array_cache could be left alone although I would point out that
it would make no difference in size as touched is changed to a bool to
fit pfmemalloc in
o It would still be necessary to do the object pointer tricks in slab.c
to avoid doing an excessive number of page lookups which is where much
of the complexity is
o The virt_to_slab could be replaced by looking up the page flag instead
and avoiding a level of indirection that would be pleasing
to an int and placed with struct kmem_cache
I agree that parts of the patch would be simplier although the
complexity of storing pfmemalloc within the obj pointer would probably
remain. However, the downside of requiring a page flag is very high. In
the event we increase the number of page flags - great, I'll use one but
right now I do not think the use of page flag is justified.
--
Mel Gorman
SUSE Labs
next prev parent reply other threads:[~2012-02-08 14:45 UTC|newest]
Thread overview: 75+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-02-06 22:56 [PATCH 00/15] Swap-over-NBD without deadlocking V8 Mel Gorman
2012-02-06 22:56 ` Mel Gorman
2012-02-06 22:56 ` [PATCH 01/15] mm: Serialize access to min_free_kbytes Mel Gorman
2012-02-06 22:56 ` Mel Gorman
2012-02-08 18:47 ` Rik van Riel
2012-02-08 18:47 ` Rik van Riel
2012-02-06 22:56 ` [PATCH 02/15] mm: sl[au]b: Add knowledge of PFMEMALLOC reserve pages Mel Gorman
2012-02-06 22:56 ` Mel Gorman
2012-02-07 16:27 ` Christoph Lameter
2012-02-07 16:27 ` Christoph Lameter
2012-02-08 14:45 ` Mel Gorman [this message]
2012-02-08 14:45 ` Mel Gorman
2012-02-08 15:14 ` Christoph Lameter
2012-02-08 15:14 ` Christoph Lameter
2012-02-08 16:34 ` Mel Gorman
2012-02-08 16:34 ` Mel Gorman
2012-02-08 19:49 ` Christoph Lameter
2012-02-08 19:49 ` Christoph Lameter
2012-02-08 21:23 ` Mel Gorman
2012-02-08 21:23 ` Mel Gorman
2012-02-08 22:13 ` Christoph Lameter
2012-02-08 22:13 ` Christoph Lameter
2012-02-09 12:50 ` Mel Gorman
2012-02-09 12:50 ` Mel Gorman
2012-02-09 19:53 ` Christoph Lameter
2012-02-09 19:53 ` Christoph Lameter
2012-02-10 10:26 ` Mel Gorman
2012-02-10 10:26 ` Mel Gorman
2012-02-10 21:01 ` Christoph Lameter
2012-02-10 21:01 ` Christoph Lameter
2012-02-10 22:07 ` Christoph Lameter
2012-02-10 22:07 ` Christoph Lameter
2012-02-13 10:12 ` Mel Gorman
2012-02-13 10:12 ` Mel Gorman
2012-02-13 11:10 ` Mel Gorman
2012-02-13 11:10 ` Mel Gorman
2012-02-06 22:56 ` [PATCH 03/15] mm: Introduce __GFP_MEMALLOC to allow access to emergency reserves Mel Gorman
2012-02-06 22:56 ` Mel Gorman
2012-02-06 22:56 ` [PATCH 04/15] mm: allow PF_MEMALLOC from softirq context Mel Gorman
2012-02-06 22:56 ` Mel Gorman
2012-02-06 22:56 ` [PATCH 05/15] mm: Ignore mempolicies when using ALLOC_NO_WATERMARK Mel Gorman
2012-02-06 22:56 ` Mel Gorman
2012-02-06 22:56 ` [PATCH 06/15] net: Introduce sk_allocation() to allow addition of GFP flags depending on the individual socket Mel Gorman
2012-02-06 22:56 ` Mel Gorman
2012-02-06 22:56 ` [PATCH 07/15] netvm: Allow the use of __GFP_MEMALLOC by specific sockets Mel Gorman
2012-02-06 22:56 ` Mel Gorman
2012-02-06 22:56 ` [PATCH 08/15] netvm: Allow skb allocation to use PFMEMALLOC reserves Mel Gorman
2012-02-06 22:56 ` Mel Gorman
2012-02-06 22:56 ` [PATCH 09/15] netvm: Propagate page->pfmemalloc to skb Mel Gorman
2012-02-06 22:56 ` Mel Gorman
2012-02-06 22:56 ` [PATCH 10/15] netvm: Propagate page->pfmemalloc from netdev_alloc_page " Mel Gorman
2012-02-06 22:56 ` Mel Gorman
2012-02-07 23:38 ` Alexander Duyck
2012-02-07 23:38 ` Alexander Duyck
2012-02-08 15:23 ` Mel Gorman
2012-02-08 15:23 ` Mel Gorman
2012-02-06 22:56 ` [PATCH 11/15] netvm: Set PF_MEMALLOC as appropriate during SKB processing Mel Gorman
2012-02-06 22:56 ` Mel Gorman
2012-02-06 22:56 ` [PATCH 12/15] mm: Micro-optimise slab to avoid a function call Mel Gorman
2012-02-06 22:56 ` Mel Gorman
2012-02-06 22:56 ` [PATCH 13/15] nbd: Set SOCK_MEMALLOC for access to PFMEMALLOC reserves Mel Gorman
2012-02-06 22:56 ` Mel Gorman
2012-02-06 22:56 ` [PATCH 14/15] mm: Throttle direct reclaimers if PF_MEMALLOC reserves are low and swap is backed by network storage Mel Gorman
2012-02-06 22:56 ` Mel Gorman
2012-02-06 22:56 ` [PATCH 15/15] mm: Account for the number of times direct reclaimers get throttled Mel Gorman
2012-02-06 22:56 ` Mel Gorman
2012-02-07 12:45 ` [PATCH 00/15] Swap-over-NBD without deadlocking V8 Hillf Danton
2012-02-07 12:45 ` Hillf Danton
2012-02-07 13:27 ` Mel Gorman
2012-02-07 13:27 ` Mel Gorman
2012-02-07 13:27 ` Mel Gorman
2012-02-08 12:51 ` Hillf Danton
2012-02-08 12:51 ` Hillf Danton
2012-02-08 15:26 ` Mel Gorman
2012-02-08 15:26 ` Mel Gorman
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