linux-kernel - Re: [RFC 01/10] autonuma: Fix watermark checking in migrate_balanced

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Date:   Fri, 1 Nov 2019 11:11:45 +0000
From:   Mel Gorman <mgorman@...e.de>
To:     "Huang, Ying" <ying.huang@...el.com>
Cc:     Peter Zijlstra <peterz@...radead.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>, Rik van Riel <riel@...hat.com>,
        Ingo Molnar <mingo@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Fengguang Wu <fengguang.wu@...el.com>
Subject: Re: [RFC 01/10] autonuma: Fix watermark checking in
 migrate_balanced_pgdat()

On Fri, Nov 01, 2019 at 03:57:18PM +0800, Huang, Ying wrote:
> From: Huang Ying <ying.huang@...el.com>
> 
> When zone_watermark_ok() is called in migrate_balanced_pgdat() to
> check migration target node, the parameter classzone_idx (for
> requested zone) is specified as 0 (ZONE_DMA).  But when allocating
> memory for autonuma in alloc_misplaced_dst_page(), the requested zone
> from GFP flags is ZONE_MOVABLE.  That is, the requested zone is
> different.  The size of lowmem_reserve for the different requested
> zone is different.  And this may cause some issues.
> 
> For example, in the zoneinfo of a test machine as below,
> 
> Node 0, zone    DMA32
>   pages free     61592
>         min      29
>         low      454
>         high     879
>         spanned  1044480
>         present  442306
>         managed  425921
>         protection: (0, 0, 62457, 62457, 62457)
> 
> The free page number of ZONE_DMA32 is greater than "high watermark +
> lowmem_reserve[ZONE_DMA]", but less than "high watermark +
> lowmem_reserve[ZONE_MOVABLE]".  And because __alloc_pages_node() in
> alloc_misplaced_dst_page() requests ZONE_MOVABLE, the
> zone_watermark_ok() on ZONE_DMA32 in migrate_balanced_pgdat() may
> always return true.  So, autonuma may not stop even when memory
> pressure in node 0 is heavy.
> 
> To fix the issue, ZONE_MOVABLE is used as parameter to call
> zone_watermark_ok() in migrate_balanced_pgdat().  This makes it same
> as requested zone in alloc_misplaced_dst_page().  So that
> migrate_balanced_pgdat() returns false when memory pressure is heavy.
> 
> Signed-off-by: "Huang, Ying" <ying.huang@...el.com>

Acked-by: Mel Gorman <mgorman@...e.de>

This patch is independent of the series and should be resent separately.
Alternatively Andrew, please pick this patch up on its own.

-- 
Mel Gorman
SUSE Labs