This patch is part of previous series: https://lore.kernel.org/lkml/20190531064313.193437-1-minchan@xxxxxxxxxx/ Originally, it was created for external madvise hinting feature. https://lkml.org/lkml/2019/5/31/463 Michal wanted to separte the discussion from external hinting interface so this patchset includes only first part of my entire patchset - introduce MADV_COLD and MADV_PAGEOUT hint to madvise. However, I keep entire description for others for easier understanding why this kinds of hint was born. Thanks. This patchset is against on next-20190712. Below is description of previous entire patchset. ================= &< ===================== - 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. To achieve the goal, the patchset introduce two new options for madvise. One is MADV_COLD which will deactivate activated pages and the other is MADV_PAGEOUT 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_PAGEOUT 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_COLD 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. * v4 - http://lore.kernel.org/lkml/20190711012528.176050-1-minchan@xxxxxxxxxx/ * v3 - http://lore.kernel.org/lkml/20190627115405.255259-1-minchan@xxxxxxxxxx * v2 - http://lore.kernel.org/lkml/20190610111252.239156-1-minchan@xxxxxxxxxx * v1 - http://lore.kernel.org/lkml/20190603053655.127730-1-minchan@xxxxxxxxxx Minchan Kim (5): mm: introduce MADV_COLD mm: change PAGEREF_RECLAIM_CLEAN with PAGE_REFRECLAIM mm: account nr_isolated_xxx in [isolate|putback]_lru_page mm: introduce MADV_PAGEOUT mm: factor out common parts between MADV_COLD and MADV_PAGEOUT include/linux/swap.h | 2 + include/uapi/asm-generic/mman-common.h | 2 + mm/compaction.c | 2 - mm/gup.c | 7 +- mm/internal.h | 2 +- mm/khugepaged.c | 3 - mm/madvise.c | 274 ++++++++++++++++++++++++- mm/memory-failure.c | 3 - mm/memory_hotplug.c | 4 - mm/mempolicy.c | 6 +- mm/migrate.c | 37 +--- mm/oom_kill.c | 2 +- mm/swap.c | 42 ++++ mm/vmscan.c | 83 +++++++- 14 files changed, 404 insertions(+), 65 deletions(-) -- 2.22.0.510.g264f2c817a-goog
