From: Christoph Lameter <cl@linux.com>
To: Mel Gorman <mgorman@suse.de>
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>,
Pekka Enberg <penberg@cs.helsinki.fi>
Subject: Re: [PATCH 02/15] mm: sl[au]b: Add knowledge of PFMEMALLOC reserve pages
Date: Wed, 8 Feb 2012 16:13:15 -0600 (CST) [thread overview]
Message-ID: <alpine.DEB.2.00.1202081557540.5970@router.home> (raw)
In-Reply-To: <20120208212323.GM5938@suse.de>
On Wed, 8 Feb 2012, Mel Gorman wrote:
> On Wed, Feb 08, 2012 at 01:49:05PM -0600, Christoph Lameter wrote:
> > On Wed, 8 Feb 2012, Mel Gorman wrote:
> >
> > > Ok, I looked into what is necessary to replace these with checking a page
> > > flag and the cost shifts quite a bit and ends up being more expensive.
> >
> > That is only true if you go the slab route.
>
> Well, yes but both slab and slub have to be supported. I see no reason
> why I would choose to make this a slab-only or slub-only feature. Slob is
> not supported because it's not expected that a platform using slob is also
> going to use network-based swap.
I think so far the patches in particular to slab.c are pretty significant
in impact.
> > Slab suffers from not having
> > the page struct pointer readily available. The changes are likely already
> > impacting slab performance without the virt_to_page patch.
> >
>
> The performance impact only comes into play when swap is on a network
> device and pfmemalloc reserves are in use. The rest of the time the check
> on ac avoids all the cost and there is a micro-optimisation later to avoid
> calling a function (patch 12).
We have been down this road too many times. Logic is added to critical
paths and memory structures grow. This is not free. And for NBD swap
support? Pretty exotic use case.
> Ok, are you asking that I use the page flag for slub and leave kmem_cache_cpu
> alone in the slub case? I can certainly check it out if that's what you
> are asking for.
No I am not asking for something. Still thinking about the best way to
address the issues. I think we can easily come up with a minimally
invasive patch for slub. Not sure about slab at this point. I think we
could avoid most of the new fields but this requires some tinkering. I
have a day @ home tomorrow which hopefully gives me a chance to
put some focus on this issue.
> I did come up with a way: the necessary information is in ac and slabp
> on slab :/ . There are not exactly many ways that the information can
> be recorded.
Wish we had something that would not involve increasing the number of
fields in these slab structures.
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next prev parent reply other threads:[~2012-02-08 22:31 UTC|newest]
Thread overview: 37+ 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 ` [PATCH 01/15] mm: Serialize access to min_free_kbytes Mel Gorman
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
2012-02-07 16:27 ` Christoph Lameter
2012-02-08 14:45 ` Mel Gorman
2012-02-08 15:14 ` Christoph Lameter
2012-02-08 16:34 ` Mel Gorman
2012-02-08 19:49 ` Christoph Lameter
2012-02-08 21:23 ` Mel Gorman
2012-02-08 22:13 ` Christoph Lameter [this message]
2012-02-09 12:50 ` Mel Gorman
2012-02-09 19:53 ` Christoph Lameter
2012-02-10 10:26 ` Mel Gorman
2012-02-10 21:01 ` Christoph Lameter
2012-02-10 22:07 ` Christoph Lameter
2012-02-13 10:12 ` 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 ` [PATCH 04/15] mm: allow PF_MEMALLOC from softirq context 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 ` [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 ` [PATCH 07/15] netvm: Allow the use of __GFP_MEMALLOC by specific sockets 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 ` [PATCH 09/15] netvm: Propagate page->pfmemalloc to skb Mel Gorman
2012-02-06 22:56 ` [PATCH 10/15] netvm: Propagate page->pfmemalloc from netdev_alloc_page " Mel Gorman
2012-02-07 23:38 ` Alexander Duyck
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 ` [PATCH 12/15] mm: Micro-optimise slab to avoid a function call 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 ` [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 ` [PATCH 15/15] mm: Account for the number of times direct reclaimers get throttled Mel Gorman
2012-02-07 12:45 ` [PATCH 00/15] Swap-over-NBD without deadlocking V8 Hillf Danton
2012-02-07 13:27 ` Mel Gorman
2012-02-08 12:51 ` Hillf Danton
2012-02-08 15:26 ` Mel Gorman
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