From: Oscar Salvador <osalvador@suse.de>
To: Dave Hansen <dave.hansen@linux.intel.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
ben.widawsky@intel.com, rientjes@google.com, cl@linux.com,
alex.shi@linux.alibaba.com, dwagner@suse.de, tobin@kernel.org,
akpm@linux-foundation.org, ying.huang@intel.com,
dan.j.williams@intel.com, cai@lca.pw, stable@vger.kernel.org
Subject: Re: [RFC][PATCH 01/13] mm/vmscan: restore zone_reclaim_mode ABI
Date: Wed, 10 Feb 2021 10:42:28 +0100 [thread overview]
Message-ID: <20210210094222.GA27173@linux> (raw)
In-Reply-To: <20210126003412.59594AA9@viggo.jf.intel.com>
On Mon, Jan 25, 2021 at 04:34:13PM -0800, Dave Hansen wrote:
>
> From: Dave Hansen <dave.hansen@linux.intel.com>
>
> I went to go add a new RECLAIM_* mode for the zone_reclaim_mode
> sysctl. Like a good kernel developer, I also went to go update the
> documentation. I noticed that the bits in the documentation didn't
> match the bits in the #defines.
>
> The VM never explicitly checks the RECLAIM_ZONE bit. The bit is,
> however implicitly checked when checking 'node_reclaim_mode==0'.
> The RECLAIM_ZONE #define was removed in a cleanup. That, by itself
> is fine.
>
> But, when the bit was removed (bit 0) the _other_ bit locations also
> got changed. That's not OK because the bit values are documented to
> mean one specific thing and users surely rely on them meaning that one
> thing and not changing from kernel to kernel. The end result is that
> if someone had a script that did:
>
> sysctl vm.zone_reclaim_mode=1
>
> This script would have gone from enalbing node reclaim for clean
> unmapped pages to writing out pages during node reclaim after the
> commit in question. That's not great.
>
> Put the bits back the way they were and add a comment so something
> like this is a bit harder to do again. Update the documentation to
> make it clear that the first bit is ignored.
>
> Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
> Fixes: 648b5cf368e0 ("mm/vmscan: remove unused RECLAIM_OFF/RECLAIM_ZONE")
> Reviewed-by: Ben Widawsky <ben.widawsky@intel.com>
> Acked-by: David Rientjes <rientjes@google.com>
> Acked-by: Christoph Lameter <cl@linux.com>
> Cc: Alex Shi <alex.shi@linux.alibaba.com>
> Cc: Daniel Wagner <dwagner@suse.de>
> Cc: "Tobin C. Harding" <tobin@kernel.org>
> Cc: Christoph Lameter <cl@linux.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Huang Ying <ying.huang@intel.com>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: Qian Cai <cai@lca.pw>
> Cc: Daniel Wagner <dwagner@suse.de>
> Cc: osalvador <osalvador@suse.de>
> Cc: stable@vger.kernel.org
Reviewed-by: Oscar Salvador <osalvador@suse.de>
>
> --
>
> Changes from v2:
> * Update description to indicate that bit0 was used for clean
> unmapped page node reclaim.
> ---
>
> b/Documentation/admin-guide/sysctl/vm.rst | 10 +++++-----
> b/mm/vmscan.c | 9 +++++++--
> 2 files changed, 12 insertions(+), 7 deletions(-)
>
> diff -puN Documentation/admin-guide/sysctl/vm.rst~mm-vmscan-restore-old-zone_reclaim_mode-abi Documentation/admin-guide/sysctl/vm.rst
> --- a/Documentation/admin-guide/sysctl/vm.rst~mm-vmscan-restore-old-zone_reclaim_mode-abi 2021-01-25 16:23:06.048866718 -0800
> +++ b/Documentation/admin-guide/sysctl/vm.rst 2021-01-25 16:23:06.056866718 -0800
> @@ -978,11 +978,11 @@ that benefit from having their data cach
> left disabled as the caching effect is likely to be more important than
> data locality.
>
> -zone_reclaim may be enabled if it's known that the workload is partitioned
> -such that each partition fits within a NUMA node and that accessing remote
> -memory would cause a measurable performance reduction. The page allocator
> -will then reclaim easily reusable pages (those page cache pages that are
> -currently not used) before allocating off node pages.
> +Consider enabling one or more zone_reclaim mode bits if it's known that the
> +workload is partitioned such that each partition fits within a NUMA node
> +and that accessing remote memory would cause a measurable performance
> +reduction. The page allocator will take additional actions before
> +allocating off node pages.
>
> Allowing zone reclaim to write out pages stops processes that are
> writing large amounts of data from dirtying pages on other nodes. Zone
> diff -puN mm/vmscan.c~mm-vmscan-restore-old-zone_reclaim_mode-abi mm/vmscan.c
> --- a/mm/vmscan.c~mm-vmscan-restore-old-zone_reclaim_mode-abi 2021-01-25 16:23:06.052866718 -0800
> +++ b/mm/vmscan.c 2021-01-25 16:23:06.057866718 -0800
> @@ -4086,8 +4086,13 @@ module_init(kswapd_init)
> */
> int node_reclaim_mode __read_mostly;
>
> -#define RECLAIM_WRITE (1<<0) /* Writeout pages during reclaim */
> -#define RECLAIM_UNMAP (1<<1) /* Unmap pages during reclaim */
> +/*
> + * These bit locations are exposed in the vm.zone_reclaim_mode sysctl
> + * ABI. New bits are OK, but existing bits can never change.
> + */
> +#define RECLAIM_ZONE (1<<0) /* Run shrink_inactive_list on the zone */
> +#define RECLAIM_WRITE (1<<1) /* Writeout pages during reclaim */
> +#define RECLAIM_UNMAP (1<<2) /* Unmap pages during reclaim */
>
> /*
> * Priority for NODE_RECLAIM. This determines the fraction of pages
> _
>
--
Oscar Salvador
SUSE L3
next prev parent reply other threads:[~2021-02-10 9:42 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-26 0:34 [RFC][PATCH 00/13] [v5] Migrate Pages in lieu of discard Dave Hansen
2021-01-26 0:34 ` [RFC][PATCH 01/13] mm/vmscan: restore zone_reclaim_mode ABI Dave Hansen
2021-02-10 9:42 ` Oscar Salvador [this message]
2021-01-26 0:34 ` [RFC][PATCH 02/13] mm/vmscan: move RECLAIM* bits to uapi header Dave Hansen
2021-02-10 9:44 ` Oscar Salvador
2021-01-26 0:34 ` [RFC][PATCH 03/13] mm/vmscan: replace implicit RECLAIM_ZONE checks with explicit checks Dave Hansen
2021-01-31 1:10 ` David Rientjes
2021-02-10 9:54 ` Oscar Salvador
2021-01-26 0:34 ` [RFC][PATCH 04/13] mm/numa: node demotion data structure and lookup Dave Hansen
2021-01-31 1:19 ` David Rientjes
2021-02-01 17:49 ` Dave Hansen
2021-01-26 0:34 ` [RFC][PATCH 05/13] mm/numa: automatically generate node migration order Dave Hansen
2021-01-29 20:46 ` Yang Shi
2021-02-01 19:13 ` Dave Hansen
2021-02-02 11:43 ` Oscar Salvador
2021-02-02 17:46 ` Yang Shi
2021-02-03 0:43 ` Dave Hansen
2021-02-04 0:26 ` Yang Shi
2021-01-26 0:34 ` [RFC][PATCH 06/13] mm/migrate: update migration order during on hotplug events Dave Hansen
2021-01-29 20:59 ` Yang Shi
2021-02-02 11:42 ` Oscar Salvador
2021-02-09 23:45 ` Dave Hansen
2021-02-10 8:55 ` Oscar Salvador
2021-01-26 0:34 ` [RFC][PATCH 07/13] mm/migrate: make migrate_pages() return nr_succeeded Dave Hansen
2021-01-29 21:04 ` Yang Shi
2021-02-09 23:41 ` Dave Hansen
2021-01-26 0:34 ` [RFC][PATCH 08/13] mm/migrate: demote pages during reclaim Dave Hansen
2021-02-02 11:55 ` Oscar Salvador
2021-02-02 22:45 ` Yang Shi
2021-02-02 22:56 ` Dave Hansen
2021-02-02 18:22 ` Yang Shi
2021-02-02 18:34 ` Dave Hansen
2021-01-26 0:34 ` [RFC][PATCH 09/13] mm/vmscan: add page demotion counter Dave Hansen
2021-01-26 0:34 ` [RFC][PATCH 10/13] mm/vmscan: add helper for querying ability to age anonymous pages Dave Hansen
2021-01-26 0:34 ` [RFC][PATCH 11/13] mm/vmscan: Consider anonymous pages without swap Dave Hansen
2021-02-02 18:56 ` Yang Shi
2021-02-02 21:35 ` Dave Hansen
2021-02-02 22:35 ` Yang Shi
2021-01-26 0:34 ` [RFC][PATCH 12/13] mm/vmscan: never demote for memcg reclaim Dave Hansen
2021-01-26 0:34 ` [RFC][PATCH 13/13] mm/migrate: new zone_reclaim_mode to enable reclaim migration Dave Hansen
2021-01-31 1:13 ` [RFC][PATCH 00/13] [v5] Migrate Pages in lieu of discard David Rientjes
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