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, so I suppose both the trashing approach and pick 25% used slab approach don't help. The per-cpu partial list flushes the whole per-cpu partial list after s->cpu_partial objects are freed, this is a little aggressive, because the per-cpu partial list need refilled again soon after an allocation. I had experiment to have separate per-cpu alloc/free partial list, which can avoid this. but again, I didn't see any workload still suffering list lock issue even with netperf which stress slub much. did you see such workload? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>