On 02/15/2013 05:21 PM, Seiji Aguchi wrote: > Rik, Satoru, > > Do you have any comments? > > Seiji Hmm, this seems what we wanted to know in the previous thread. Because extra_free_kbytes is quite simple and it fixes the problem, it should be merged into upstream. Regards, Satoru >> -----Original Message----- >> From: linux-kernel-owner@xxxxxxxxxxxxxxx >> [mailto:linux-kernel-owner@xxxxxxxxxxxxxxx] On Behalf Of dormando >> Sent: Monday, February 11, 2013 9:01 PM >> To: Rik van Riel >> Cc: Randy Dunlap; Satoru Moriya; linux-kernel@xxxxxxxxxxxxxxx; >> linux-mm@xxxxxxxxx; lwoodman@xxxxxxxxxx; Seiji Aguchi; >> akpm@xxxxxxxxxxxxxxxxxxxx; hughd@xxxxxxxxxx >> Subject: extra free kbytes tunable >> >> Hi, >> >> As discussed in this thread: >> http://marc.info/?l=linux-mm&m=131490523222031&w=2 >> (with this cleanup as well: https://lkml.org/lkml/2011/9/2/225) >> >> A tunable was proposed to allow specifying the distance between >> pages_min and the low watermark before kswapd is kicked in to free up >> pages. I'd like to re-open this thread since the patch did not appear to go anywhere. >> >> We have a server workload wherein machines with 100G+ of "free" >> memory (used by page cache), scattered but frequent random io reads >> from 12+ SSD's, and 5gbps+ of internet traffic, will frequently hit >> direct reclaim in a few different ways. >> >> 1) It'll run into small amounts of reclaim randomly (a few hundred thousand). >> >> 2) A burst of reads or traffic can cause extra pressure, which kswapd >> occasionally responds to by freeing up 40g+ of the pagecache all at >> once >> (!) while pausing the system (Argh). >> >> 3) A blip in an upstream provider or failover from a peer causes the >> kernel to allocate massive amounts of memory for retransmission >> queues/etc, potentially along with buffered IO reads and (some, but >> not often a ton) of new allocations from an application. This paired >> with 2) can cause the box to stall for 15+ seconds. >> >> We're seeing this more in 3.4/3.5/3.6, saw it less in 2.6.38. Mass >> reclaims are more common in newer kernels, but reclaims still happen >> in all kernels without raising min_free_kbytes dramatically. >> >> I've found that setting "lowmem_reserve_ratio" to something like "1 1 32" >> (thus protecting the DMA32 zone) causes 2) to happen less often, and >> is generally less violent with 1). >> >> Setting min_free_kbytes to 15G or more, paired with the above, has >> been the best at mitigating the issue. This is simply trying to raise >> the distance between the min and low watermarks. With min_free_kbytes >> set to 15000000, that gives us a whopping 1.8G (!!!) of leeway before >> slamming into direct reclaim. >> >> So, this patch is unfortunate but wonderful at letting us reclaim >> 10G+ of otherwise lost memory. Could we please revisit it? >> >> I saw a lot of discussion on doing this automatically, or making >> kswapd more efficient to it, and I'd love to do that. Beyond making >> kswapd psychic I haven't seen any better options yet. >> >> The issue is more complex than simply having an application warn of >> an impending allocation, since this can happen via read load on disk >> or from kernel page allocations for the network, or a combination of >> the two (or three, if you add the app back in). >> >> It's going to get worse as we push machines with faster SSD's and >> bigger networks. I'm open to any ideas on how to make kswapd more >> efficient in our case, or really anything at all that works. >> >> I have more details, but cut it down as much as I could for this mail. >> >> Thanks, >> -Dormando >> -- >> To unsubscribe from this list: send the line "unsubscribe >> linux-kernel" in the body of a message to majordomo@xxxxxxxxxxxxxxx >> More majordomo info at http://vger.kernel.org/majordomo-info.html >> Please read the FAQ at http://www.tux.org/lkml/ > > -- > 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/ . > Don't email: <a href=ilto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a> ��.n������g��� �a��� �&ޖ)���)��h���&������梷���� �Ǟ�m������)������^�����������v���O��zf������