From: Johannes Weiner <hannes@cmpxchg.org>
To: Minchan Kim <minchan@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
linux-mm <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>,
linux-api@vger.kernel.org, Michal Hocko <mhocko@suse.com>,
Tim Murray <timmurray@google.com>,
Joel Fernandes <joel@joelfernandes.org>,
Suren Baghdasaryan <surenb@google.com>,
Daniel Colascione <dancol@google.com>,
Shakeel Butt <shakeelb@google.com>,
Sonny Rao <sonnyrao@google.com>,
oleksandr@redhat.com, hdanton@sina.com, lizeb@google.com,
Dave Hansen <dave.hansen@intel.com>,
"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
Subject: Re: [PATCH v4 1/4] mm: introduce MADV_COLD
Date: Thu, 11 Jul 2019 11:25:55 -0400 [thread overview]
Message-ID: <20190711152555.GB20341@cmpxchg.org> (raw)
In-Reply-To: <20190711012528.176050-2-minchan@kernel.org>
On Thu, Jul 11, 2019 at 10:25:25AM +0900, Minchan Kim wrote:
> When a process expects no accesses to a certain memory range, it could
> give a hint to kernel that the pages can be reclaimed when memory pressure
> happens but data should be preserved for future use. This could reduce
> workingset eviction so it ends up increasing performance.
>
> This patch introduces the new MADV_COLD hint to madvise(2) syscall.
> MADV_COLD can be used by a process to mark a memory range as not expected
> to be used in the near future. The hint can help kernel in deciding which
> pages to evict early during memory pressure.
>
> It works for every LRU pages like MADV_[DONTNEED|FREE]. IOW, It moves
>
> active file page -> inactive file LRU
> active anon page -> inacdtive anon LRU
>
> Unlike MADV_FREE, it doesn't move active anonymous pages to inactive
> file LRU's head because MADV_COLD is a little bit different symantic.
> MADV_FREE means it's okay to discard when the memory pressure because
> the content of the page is *garbage* so freeing such pages is almost zero
> overhead since we don't need to swap out and access afterward causes just
> minor fault. Thus, it would make sense to put those freeable pages in
> inactive file LRU to compete other used-once pages. It makes sense for
> implmentaion point of view, too because it's not swapbacked memory any
> longer until it would be re-dirtied. Even, it could give a bonus to make
> them be reclaimed on swapless system. However, MADV_COLD doesn't mean
> garbage so reclaiming them requires swap-out/in in the end so it's bigger
> cost. Since we have designed VM LRU aging based on cost-model, anonymous
> cold pages would be better to position inactive anon's LRU list, not file
> LRU. Furthermore, it would help to avoid unnecessary scanning if system
> doesn't have a swap device. Let's start simpler way without adding
> complexity at this moment. However, keep in mind, too that it's a caveat
> that workloads with a lot of pages cache are likely to ignore MADV_COLD
> on anonymous memory because we rarely age anonymous LRU lists.
>
> * man-page material
>
> MADV_COLD (since Linux x.x)
>
> Pages in the specified regions will be treated as less-recently-accessed
> compared to pages in the system with similar access frequencies.
> In contrast to MADV_FREE, the contents of the region are preserved
> regardless of subsequent writes to pages.
>
> MADV_COLD cannot be applied to locked pages, Huge TLB pages, or VM_PFNMAP
> pages.
>
> * v2
> * add up the warn with lots of page cache workload - mhocko
> * add man page stuff - dave
>
> * v1
> * remove page_mapcount filter - hannes, mhocko
> * remove idle page handling - joelaf
>
> * RFCv2
> * add more description - mhocko
>
> * RFCv1
> * renaming from MADV_COOL to MADV_COLD - hannes
>
> * internal review
> * use clear_page_youn in deactivate_page - joelaf
> * Revise the description - surenb
> * Renaming from MADV_WARM to MADV_COOL - surenb
>
> Acked-by: Michal Hocko <mhocko@suse.com>
> Signed-off-by: Minchan Kim <minchan@kernel.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
next prev parent reply other threads:[~2019-07-11 15:26 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-11 1:25 [PATCH v4 0/4] Introduce MADV_COLD and MADV_PAGEOUT Minchan Kim
2019-07-11 1:25 ` [PATCH v4 1/4] mm: introduce MADV_COLD Minchan Kim
2019-07-11 15:25 ` Johannes Weiner [this message]
2019-07-11 1:25 ` [PATCH v4 2/4] mm: change PAGEREF_RECLAIM_CLEAN with PAGE_REFRECLAIM Minchan Kim
2019-07-11 1:25 ` [PATCH v4 3/4] mm: account nr_isolated_xxx in [isolate|putback]_lru_page Minchan Kim
2019-07-11 18:07 ` Johannes Weiner
2019-07-11 1:25 ` [PATCH v4 4/4] mm: introduce MADV_PAGEOUT Minchan Kim
2019-07-11 18:42 ` Johannes Weiner
2019-07-12 5:18 ` Minchan Kim
2019-07-12 7:19 ` Michal Hocko
2019-07-12 13:58 ` Johannes Weiner
2019-07-12 15:01 ` Michal Hocko
2019-07-14 23:11 ` Minchan Kim
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