From: Andrew Morton <akpm@linux-foundation.org>
To: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Vlastimil Babka <vbabka@suse.cz>,
Mel Gorman <mgorman@techsingularity.net>,
linux-mm <linux-mm@kvack.org>
Subject: Re: [PATCH] mm/page_alloc: don't wake up kswapd from rmqueue() unless __GFP_KSWAPD_RECLAIM is specified
Date: Thu, 11 May 2023 20:45:07 -0700 [thread overview]
Message-ID: <20230511204507.fbcc234616378b3c28599712@linux-foundation.org> (raw)
In-Reply-To: <6d6fb601-6100-92b9-cea3-e7ebacc7693a@I-love.SAKURA.ne.jp>
On Thu, 11 May 2023 22:47:36 +0900 Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> wrote:
> Commit 73444bc4d8f9 ("mm, page_alloc: do not wake kswapd with zone lock
> held") moved wakeup_kswapd() from steal_suitable_fallback() to rmqueue()
> using ZONE_BOOSTED_WATERMARK flag. But since zone->flags is a shared
> variable, a thread doing !__GFP_KSWAPD_RECLAIM allocation request might
> observe this flag being set immediately after another thread doing
> __GFP_KSWAPD_RECLAIM allocation request set this flag.
What are the user-visible runtime effects of this flaw?
> Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.j
> +++ b/mm/page_alloc.c
> @@ -3052,7 +3052,8 @@ struct page *rmqueue(struct zone *preferred_zone,
>
> out:
> /* Separate test+clear to avoid unnecessary atomics */
> - if (unlikely(test_bit(ZONE_BOOSTED_WATERMARK, &zone->flags))) {
> + if (unlikely(test_bit(ZONE_BOOSTED_WATERMARK, &zone->flags))
> + && (alloc_flags & ALLOC_KSWAPD)) {
> clear_bit(ZONE_BOOSTED_WATERMARK, &zone->flags);
> wakeup_kswapd(zone, 0, 0, zone_idx(zone));
> }
Thanks, I'll queue this up for some testing while awaiting input from
Mel.
next prev parent reply other threads:[~2023-05-12 3:45 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-11 13:47 [PATCH] mm/page_alloc: don't wake up kswapd from rmqueue() unless __GFP_KSWAPD_RECLAIM is specified Tetsuo Handa
2023-05-12 3:45 ` Andrew Morton [this message]
2023-05-13 9:38 ` Tetsuo Handa
2023-05-13 10:23 ` Mel Gorman
2023-05-14 0:28 ` [PATCH v2] mm/page_alloc: don't wake " Tetsuo Handa
2023-05-15 6:03 ` Huang, Ying
2023-05-15 6:35 ` Huang, Ying
2023-05-15 7:38 ` Mel Gorman
2023-05-15 10:17 ` Tetsuo Handa
2023-05-16 1:44 ` Huang, Ying
2023-05-22 13:57 ` Tetsuo Handa
2023-05-22 14:58 ` Mel Gorman
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