(cc linux-mm, where all the suckiness ends up) On Mon, 15 Nov 2010 11:52:46 -0800 Simon Kirby <sim@xxxxxxxxxx> wrote: > Hi! > > We're seeing cases on a number of servers where cache never fully grows > to use all available memory. Sometimes we see servers with 4 GB of > memory that never seem to have less than 1.5 GB free, even with a > constantly-active VM. In some cases, these servers also swap out while > this happens, even though they are constantly reading the working set > into memory. We have been seeing this happening for a long time; > I don't think it's anything recent, and it still happens on 2.6.36. > > I noticed that CONFIG_NUMA seems to enable some more complicated > reclaiming bits and figured it might help since most stock kernels seem > to ship with it now. This seems to have helped, but it may just be > wishful thinking. We still see this happening, though maybe to a lesser > degree. (The following observations are with CONFIG_NUMA enabled.) > > I was eyeballing "vmstat 1" and "watch -n.2 -d cat /proc/vmstat" at the > same time, and I can see distinctly that the page cache is growing nicely > until a sudden event where 400 MB is freed within 1 second, leaving > this particular box with 700 MB free again. kswapd numbers increase in > /proc/vmstat, which leads me to believe that __alloc_pages_slowpath() has > been called, since it seems to be the thing that wakes up kswapd. > > Previous patterns and watching of "vmstat 1" show that the swapping out > also seems to occur during the times that memory is quickly freed. > > These are all x86_64, and so there is no highmem garbage going on. > The only zones would be for DMA, right? Is the combination of memory > fragmentation and large-order allocations the only thing that would be > causing this reclaim here? Is there some easy bake knob for finding what > is causing the free memory jumps each time this happens? > > Kernel config and munin graph of free memory here: > > http://0x.ca/sim/ref/2.6.36/ > > I notice CONFIG_COMPACTION is still "EXPERIMENTAL". Would it be worth > trying here? It seems to enable defrag before reclaim, but that sounds > kind of ...complicated... > > Cheers, > > Simon- > > procs -----------memory---------- ---swap-- -----io---- -system-- ----cpu---- > r b swpd free buff cache si so bi bo in cs us sy id wa > 1 0 11496 401684 40364 2531844 0 0 4540 773 7890 16291 13 9 77 1 > 3 0 11492 400180 40372 2534204 0 0 5572 699 8544 14856 25 9 66 1 > 0 0 11492 394344 40372 2540796 0 0 5256 345 8239 16723 17 7 73 2 > 0 0 11492 388524 40372 2546236 0 0 5216 393 8687 17289 14 9 76 1 > 4 1 11684 716296 40244 2218612 0 220 6868 1837 11124 27368 28 20 51 0 > 1 0 11732 753992 40248 2181468 0 120 5240 647 9542 15609 38 11 50 1 > 1 0 11712 736864 40260 2197788 0 0 5872 9147 9838 16373 41 11 47 1 > 0 0 11712 738096 40260 2196984 0 0 4628 493 7980 15536 22 10 67 1 > 2 0 11712 733508 40260 2201756 0 0 4404 418 7265 16867 10 9 80 2 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>