Re: [PATCH v3 0/5] Introduce MADV_COLD and MADV_PAGEOUT

[Minchan Kim <minchan@kernel.org>]

Hi Folks,

Do you guys have comments? I think it would be long enough to be
pending. If there is no further comments, I want to ask to merge.

Thanks.

On Thu, Jun 27, 2019 at 08:54:00PM +0900, Minchan Kim wrote:
> This patch is part of previous series:
> https://lore.kernel.org/lkml/20190531064313.193437-1-minchan@kernel.org/T/#u
> 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-20190530.
> 
> 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.
> 
> 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 pmd young/dirty bit handling and THP split
> 
>  include/linux/huge_mm.h                |   3 -
>  include/linux/swap.h                   |   2 +
>  include/uapi/asm-generic/mman-common.h |   2 +
>  mm/compaction.c                        |   2 -
>  mm/gup.c                               |   7 +-
>  mm/huge_memory.c                       |  74 -----
>  mm/internal.h                          |   2 +-
>  mm/khugepaged.c                        |   3 -
>  mm/madvise.c                           | 438 ++++++++++++++++++++++++-
>  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                            |  86 ++++-
>  16 files changed, 566 insertions(+), 147 deletions(-)
> 
> -- 
> 2.22.0.410.gd8fdbe21b5-goog
>