On Tue, 2017-10-17 at 13:32 +0200, Vlastimil Babka wrote: > On 10/13/2017 08:31 AM, Aaron Lu wrote: > > __rmqueue(), __rmqueue_fallback(), __rmqueue_smallest() and > > __rmqueue_cma_fallback() are all in page allocator's hot path and > > better be finished as soon as possible. One way to make them faster > > is by making them inline. But as Andrew Morton and Andi Kleen pointed > > out: > > https://lkml.org/lkml/2017/10/10/1252 > > https://lkml.org/lkml/2017/10/10/1279 > > To make sure they are inlined, we should use __always_inline for them. > > > > With the will-it-scale/page_fault1/process benchmark, when using nr_cpu > > processes to stress buddy, the results for will-it-scale.processes with > > and without the patch are: > > > > On a 2-sockets Intel-Skylake machine: > > > > compiler base head > > gcc-4.4.7 6496131 6911823 +6.4% > > gcc-4.9.4 7225110 7731072 +7.0% > > gcc-5.4.1 7054224 7688146 +9.0% > > gcc-6.2.0 7059794 7651675 +8.4% > > > > On a 4-sockets Intel-Skylake machine: > > > > compiler base head > > gcc-4.4.7 13162890 13508193 +2.6% > > gcc-4.9.4 14997463 15484353 +3.2% > > gcc-5.4.1 14708711 15449805 +5.0% > > gcc-6.2.0 14574099 15349204 +5.3% > > > > The above 4 compilers are used becuase I've done the tests through Intel's > > Linux Kernel Performance(LKP) infrastructure and they are the available > > compilers there. > > > > The benefit being less on 4 sockets machine is due to the lock contention > > there(perf-profile/native_queued_spin_lock_slowpath=81%) is less severe > > than on the 2 sockets machine(85%). > > > > What the benchmark does is: it forks nr_cpu processes and then each > > process does the following: > > 1 mmap() 128M anonymous space; > > 2 writes to each page there to trigger actual page allocation; > > 3 munmap() it. > > in a loop. > > https://github.com/antonblanchard/will-it-scale/blob/master/tests/page_fault1.c > > Are transparent hugepages enabled? If yes, __rmqueue() is called from > rmqueue(), and there's only one page fault (and __rmqueue()) per 512 > "writes to each page". If not, __rmqueue() is called from rmqueue_bulk() > in bursts once pcplists are depleted. I guess it's the latter, otherwise > I wouldn't expect a function call to have such visible overhead. THP is disabled. I should have mentioned this in the changelog, sorry about that. > > I guess what would help much more would be a bulk __rmqueue_smallest() > to grab multiple pages from the freelists. But can't argue with your Do I understand you correctly that you suggest to use a bulk __rmqueue_smallest(), say __rmqueue_smallest_bulk(). With that, instead of looping pcp->batch times in rmqueue_bulk(), a single call to __rmqueue_smallest_bulk() is enough and __rmqueue_smallest_bulk() will loop pcp->batch times to get those pages? Then it feels like __rmqueue_smallest_bulk() has become rmqueue_bulk(), or do I miss something? > numbers against this patch. > > > Binary size wise, I have locally built them with different compilers: > > > > [aaron@aaronlu obj]$ size */*/mm/page_alloc.o > > text data bss dec hex filename > > 37409 9904 8524 55837 da1d gcc-4.9.4/base/mm/page_alloc.o > > 38273 9904 8524 56701 dd7d gcc-4.9.4/head/mm/page_alloc.o > > 37465 9840 8428 55733 d9b5 gcc-5.5.0/base/mm/page_alloc.o > > 38169 9840 8428 56437 dc75 gcc-5.5.0/head/mm/page_alloc.o > > 37573 9840 8428 55841 da21 gcc-6.4.0/base/mm/page_alloc.o > > 38261 9840 8428 56529 dcd1 gcc-6.4.0/head/mm/page_alloc.o > > 36863 9840 8428 55131 d75b gcc-7.2.0/base/mm/page_alloc.o > > 37711 9840 8428 55979 daab gcc-7.2.0/head/mm/page_alloc.o > > > > Text size increased about 800 bytes for mm/page_alloc.o. > > BTW, do you know about ./scripts/bloat-o-meter? :) NO!!! Thanks for bringing this up :) > With gcc 7.2.1: > > ./scripts/bloat-o-meter base.o mm/page_alloc.o > > add/remove: 1/2 grow/shrink: 2/0 up/down: 2493/-1649 (844) Nice, it clearly showed 844 bytes bloat. > function old new delta > get_page_from_freelist 2898 4937 +2039 > steal_suitable_fallback - 365 +365 > find_suitable_fallback 31 120 +89 > find_suitable_fallback.part 115 - -115 > __rmqueue 1534 - -1534 > > > > [aaron@aaronlu obj]$ size */*/vmlinux > > text data bss dec hex filename > > 10342757 5903208 17723392 33969357 20654cd gcc-4.9.4/base/vmlinux > > 10342757 5903208 17723392 33969357 20654cd gcc-4.9.4/head/vmlinux > > 10332448 5836608 17715200 33884256 2050860 gcc-5.5.0/base/vmlinux > > 10332448 5836608 17715200 33884256 2050860 gcc-5.5.0/head/vmlinux > > 10094546 5836696 17715200 33646442 201676a gcc-6.4.0/base/vmlinux > > 10094546 5836696 17715200 33646442 201676a gcc-6.4.0/head/vmlinux > > 10018775 5828732 17715200 33562707 2002053 gcc-7.2.0/base/vmlinux > > 10018775 5828732 17715200 33562707 2002053 gcc-7.2.0/head/vmlinux > > > > Text size for vmlinux has no change though, probably due to function > > alignment. > > Yep that's useless to show. These differences do add up though, until > they eventually cross the alignment boundary. Agreed. But you know, it is the hot path, the performance improvement might be worth it.��.n������g��� �a��� �&ޖ)���)��h���&������梷���� �Ǟ�m������)������^�����������v���O��zf������
