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[213.175.37.10]) by smtp.gmail.com with ESMTPSA id o8sm32493773wra.4.2019.05.20.07.42.01 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Mon, 20 May 2019 07:42:01 -0700 (PDT) Date: Mon, 20 May 2019 16:42:00 +0200 From: Oleksandr Natalenko To: Minchan Kim Cc: Andrew Morton , LKML , linux-mm , Michal Hocko , Johannes Weiner , Tim Murray , Joel Fernandes , Suren Baghdasaryan , Daniel Colascione , Shakeel Butt , Sonny Rao , Brian Geffon Subject: Re: [RFC 0/7] introduce memory hinting API for external process Message-ID: <20190520144200.cpiqhxxbxyovmk7h@butterfly.localdomain> References: <20190520035254.57579-1-minchan@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20190520035254.57579-1-minchan@kernel.org> User-Agent: NeoMutt/20180716 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi. On Mon, May 20, 2019 at 12:52:47PM +0900, Minchan Kim wrote: > - Background > > The Android terminology used for forking a new process and starting an app > from scratch is a cold start, while resuming an existing app is a hot start. > While we continually try to improve the performance of cold starts, hot > starts will always be significantly less power hungry as well as faster so > we are trying to make hot start more likely than cold start. > > To increase hot start, Android userspace manages the order that apps should > be killed in a process called ActivityManagerService. ActivityManagerService > tracks every Android app or service that the user could be interacting with > at any time and translates that into a ranked list for lmkd(low memory > killer daemon). They are likely to be killed by lmkd if the system has to > reclaim memory. In that sense they are similar to entries in any other cache. > Those apps are kept alive for opportunistic performance improvements but > those performance improvements will vary based on the memory requirements of > individual workloads. > > - Problem > > Naturally, cached apps were dominant consumers of memory on the system. > However, they were not significant consumers of swap even though they are > good candidate for swap. Under investigation, swapping out only begins > once the low zone watermark is hit and kswapd wakes up, but the overall > allocation rate in the system might trip lmkd thresholds and cause a cached > process to be killed(we measured performance swapping out vs. zapping the > memory by killing a process. Unsurprisingly, zapping is 10x times faster > even though we use zram which is much faster than real storage) so kill > from lmkd will often satisfy the high zone watermark, resulting in very > few pages actually being moved to swap. > > - Approach > > The approach we chose was to use a new interface to allow userspace to > proactively reclaim entire processes by leveraging platform information. > This allowed us to bypass the inaccuracy of the kernel’s LRUs for pages > that are known to be cold from userspace and to avoid races with lmkd > by reclaiming apps as soon as they entered the cached state. Additionally, > it could provide many chances for platform to use much information to > optimize memory efficiency. > > IMHO we should spell it out that this patchset complements MADV_WONTNEED > and MADV_FREE by adding non-destructive ways to gain some free memory > space. MADV_COLD is similar to MADV_WONTNEED in a way that it hints the > kernel that memory region is not currently needed and should be reclaimed > immediately; MADV_COOL is similar to MADV_FREE in a way that it hints the > kernel that memory region is not currently needed and should be reclaimed > when memory pressure rises. > > To achieve the goal, the patchset introduce two new options for madvise. > One is MADV_COOL which will deactive activated pages and the other is > MADV_COLD which will reclaim private pages instantly. These new options > complement MADV_DONTNEED and MADV_FREE by adding non-destructive ways to > gain some free memory space. MADV_COLD is similar to MADV_DONTNEED in a way > that it hints the kernel that memory region is not currently needed and > should be reclaimed immediately; MADV_COOL is similar to MADV_FREE in a way > that it hints the kernel that memory region is not currently needed and > should be reclaimed when memory pressure rises. > > This approach is similar in spirit to madvise(MADV_WONTNEED), but the > information required to make the reclaim decision is not known to the app. > Instead, it is known to a centralized userspace daemon, and that daemon > must be able to initiate reclaim on its own without any app involvement. > To solve the concern, this patch introduces new syscall - > > struct pr_madvise_param { > int size; > const struct iovec *vec; > } > > int process_madvise(int pidfd, ssize_t nr_elem, int *behavior, > struct pr_madvise_param *restuls, > struct pr_madvise_param *ranges, > unsigned long flags); > > The syscall get pidfd to give hints to external process and provides > pair of result/ranges vector arguments so that it could give several > hints to each address range all at once. > > I guess others have different ideas about the naming of syscall and options > so feel free to suggest better naming. > > - Experiment > > We did bunch of testing with several hundreds of real users, not artificial > benchmark on android. We saw about 17% cold start decreasement without any > significant battery/app startup latency issues. And with artificial benchmark > which launches and switching apps, we saw average 7% app launching improvement, > 18% less lmkd kill and good stat from vmstat. > > A is vanilla and B is process_madvise. > > > A B delta ratio(%) > allocstall_dma 0 0 0 0.00 > allocstall_movable 1464 457 -1007 -69.00 > allocstall_normal 263210 190763 -72447 -28.00 > allocstall_total 264674 191220 -73454 -28.00 > compact_daemon_wake 26912 25294 -1618 -7.00 > compact_fail 17885 14151 -3734 -21.00 > compact_free_scanned 4204766409 3835994922 -368771487 -9.00 > compact_isolated 3446484 2967618 -478866 -14.00 > compact_migrate_scanned 1621336411 1324695710 -296640701 -19.00 > compact_stall 19387 15343 -4044 -21.00 > compact_success 1502 1192 -310 -21.00 > kswapd_high_wmark_hit_quickly 234 184 -50 -22.00 > kswapd_inodesteal 221635 233093 11458 5.00 > kswapd_low_wmark_hit_quickly 66065 54009 -12056 -19.00 > nr_dirtied 259934 296476 36542 14.00 > nr_vmscan_immediate_reclaim 2587 2356 -231 -9.00 > nr_vmscan_write 1274232 2661733 1387501 108.00 > nr_written 1514060 2937560 1423500 94.00 > pageoutrun 67561 55133 -12428 -19.00 > pgactivate 2335060 1984882 -350178 -15.00 > pgalloc_dma 13743011 14096463 353452 2.00 > pgalloc_movable 0 0 0 0.00 > pgalloc_normal 18742440 16802065 -1940375 -11.00 > pgalloc_total 32485451 30898528 -1586923 -5.00 > pgdeactivate 4262210 2930670 -1331540 -32.00 > pgfault 30812334 31085065 272731 0.00 > pgfree 33553970 31765164 -1788806 -6.00 > pginodesteal 33411 15084 -18327 -55.00 > pglazyfreed 0 0 0 0.00 > pgmajfault 551312 1508299 956987 173.00 > pgmigrate_fail 43927 29330 -14597 -34.00 > pgmigrate_success 1399851 1203922 -195929 -14.00 > pgpgin 24141776 19032156 -5109620 -22.00 > pgpgout 959344 1103316 143972 15.00 > pgpgoutclean 4639732 3765868 -873864 -19.00 > pgrefill 4884560 3006938 -1877622 -39.00 > pgrotated 37828 25897 -11931 -32.00 > pgscan_direct 1456037 957567 -498470 -35.00 > pgscan_direct_throttle 0 0 0 0.00 > pgscan_kswapd 6667767 5047360 -1620407 -25.00 > pgscan_total 8123804 6004927 -2118877 -27.00 > pgskip_dma 0 0 0 0.00 > pgskip_movable 0 0 0 0.00 > pgskip_normal 14907 25382 10475 70.00 > pgskip_total 14907 25382 10475 70.00 > pgsteal_direct 1118986 690215 -428771 -39.00 > pgsteal_kswapd 4750223 3657107 -1093116 -24.00 > pgsteal_total 5869209 4347322 -1521887 -26.00 > pswpin 417613 1392647 975034 233.00 > pswpout 1274224 2661731 1387507 108.00 > slabs_scanned 13686905 10807200 -2879705 -22.00 > workingset_activate 668966 569444 -99522 -15.00 > workingset_nodereclaim 38957 32621 -6336 -17.00 > workingset_refault 2816795 2179782 -637013 -23.00 > workingset_restore 294320 168601 -125719 -43.00 > > pgmajfault is increased by 173% because swapin is increased by 200% by > process_madvise hint. However, swap read based on zram is much cheaper > than file IO in performance point of view and app hot start by swapin is > also cheaper than cold start from the beginning of app which needs many IO > from storage and initialization steps. > > This patchset is against on next-20190517. > > Minchan Kim (7): > mm: introduce MADV_COOL > mm: change PAGEREF_RECLAIM_CLEAN with PAGE_REFRECLAIM > mm: introduce MADV_COLD > mm: factor out madvise's core functionality > mm: introduce external memory hinting API > mm: extend process_madvise syscall to support vector arrary > mm: madvise support MADV_ANONYMOUS_FILTER and MADV_FILE_FILTER > > arch/x86/entry/syscalls/syscall_32.tbl | 1 + > arch/x86/entry/syscalls/syscall_64.tbl | 1 + > include/linux/page-flags.h | 1 + > include/linux/page_idle.h | 15 + > include/linux/proc_fs.h | 1 + > include/linux/swap.h | 2 + > include/linux/syscalls.h | 2 + > include/uapi/asm-generic/mman-common.h | 12 + > include/uapi/asm-generic/unistd.h | 2 + > kernel/signal.c | 2 +- > kernel/sys_ni.c | 1 + > mm/madvise.c | 600 +++++++++++++++++++++---- > mm/swap.c | 43 ++ > mm/vmscan.c | 80 +++- > 14 files changed, 680 insertions(+), 83 deletions(-) > > -- > 2.21.0.1020.gf2820cf01a-goog > Please Cc me for the next iteration since I was working on the very same thing recently [1]. Thank you. [1] https://gitlab.com/post-factum/pf-kernel/commits/remote-madvise-v3 -- Best regards, Oleksandr Natalenko (post-factum) Senior Software Maintenance Engineer