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Date: Mon, 12 Dec 2011 12:48:24 +0800 From: Shaohua Li <shaohua.li@...el.com> To: "Alex,Shi" <alex.shi@...el.com> Cc: David Rientjes <rientjes@...gle.com>, Christoph Lameter <cl@...ux.com>, "penberg@...nel.org" <penberg@...nel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "linux-mm@...ck.org" <linux-mm@...ck.org>, Andi Kleen <ak@...ux.intel.com> Subject: Re: [PATCH 1/3] slub: set a criteria for slub node partial adding On Mon, 2011-12-12 at 12:25 +0800, Alex,Shi wrote: > On Mon, 2011-12-12 at 12:35 +0800, Li, Shaohua wrote: > > On Mon, 2011-12-12 at 12:14 +0800, Shi, Alex wrote: > > > On Mon, 2011-12-12 at 10:43 +0800, Li, Shaohua wrote: > > > > On Wed, 2011-12-07 at 15:28 +0800, David Rientjes wrote: > > > > > On Wed, 7 Dec 2011, Shaohua Li wrote: > > > > > > > > > > > interesting. I did similar experiment before (try to sort the page > > > > > > according to free number), but it appears quite hard. The free number of > > > > > > a page is dynamic, eg more slabs can be freed when the page is in > > > > > > partial list. And in netperf test, the partial list could be very very > > > > > > long. Can you post your patch, I definitely what to look at it. > > > > > > > > > > It was over a couple of years ago and the slub code has changed > > > > > significantly since then, but you can see the general concept of the "slab > > > > > thrashing" problem with netperf and my solution back then: > > > > > > > > > > http://marc.info/?l=linux-kernel&m=123839191416478 > > > > > http://marc.info/?l=linux-kernel&m=123839203016592 > > > > > http://marc.info/?l=linux-kernel&m=123839202916583 > > > > > > > > > > I also had a separate patchset that, instead of this approach, would just > > > > > iterate through the partial list in get_partial_node() looking for > > > > > anything where the number of free objects met a certain threshold, which > > > > > still defaulted to 25% and instantly picked it. The overhead was taking > > > > > slab_lock() for each page, but that was nullified by the performance > > > > > speedup of using the alloc fastpath a majority of the time for both > > > > > kmalloc-256 and kmalloc-2k when in the past it had only been able to serve > > > > > one or two allocs. If no partial slab met the threshold, the slab_lock() > > > > > is held of the partial slab with the most free objects and returned > > > > > instead. > > > > With the per-cpu partial list, I didn't see any workload which is still > > > > suffering from the list lock, > > > > > > The merge error that you fixed in 3.2-rc1 for hackbench regression is > > > due to add slub to node partial head. And data of hackbench show node > > > partial is still heavy used in allocation. > > The patch is already in base kernel, did you mean even with it you still > > saw the list locking issue with latest kernel? > > > > Yes, list_lock still hurt performance. It will be helpful if you can do > some optimize for it. please post data and the workload. In my test, I didn't see the locking takes significant time with perf. the slub stat you posted in last mail shows most allocation goes the fast path. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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