From: Joonwon Kang <joonwonkang@google.com>
To: joonwonkang@google.com
Cc: akpm@linux-foundation.org, cl@gentwo.org, dennis@kernel.org,
dodam@google.com, linux-kernel@vger.kernel.org,
linux-mm@kvack.org, tj@kernel.org
Subject: Re: [PATCH v2] percpu: Fix hint invariant breakage
Date: Wed, 8 Apr 2026 11:04:53 +0000 [thread overview]
Message-ID: <20260408110453.694461-1-joonwonkang@google.com> (raw)
In-Reply-To: <20260408100642.83919-1-joonwonkang@google.com>
> The invariant "scan_hint_start > contig_hint_start if and only if
> scan_hint == contig_hint" should be kept for hint management. However,
> it could be broken in some cases:
>
> - if (new contig == contig_hint == scan_hint) && (contig_hint_start <
> scan_hint_start < new contig start) && the new contig is to become a
> new contig_hint due to its better alignment, then scan_hint should
> be invalidated instead of keeping the old value.
>
> - if (new contig == contig_hint > scan_hint) && (new contig start <
> contig_hint_start) && the new contig is not to become a new
> contig_hint, then scan_hint should be not updated to the new contig.
>
> This commit refactors the percpu block update code to make it more
> visible on what to consider, e.g. when the new contig overlaps with the
> old contig_hint or scan_hint, fixes the invariant breakage and also
> optimizes scan_hint further. Some of the optimization cases when no
> overlap occurs are:
>
> - if (new contig > contig_hint > scan_hint) && (scan_hint_start < new
> contig start < contig_hint_start), then keep scan_hint instead of
> invalidating it.
>
> - if (new contig > contig_hint == scan_hint) && (contig_hint_start <
> new contig start < scan_hint_start), then update scan_hint to the
> old contig_hint instead of invalidating it.
>
> - if (new contig == contig_hint > scan_hint) && (new contig start <
> contig_hint_start) && the new contig is to become a new contig_hint
> due to its better alignment, then update scan_hint to the old
> contig_hint instead of invalidating or keeping it.
>
> Signed-off-by: Joonwon Kang <joonwonkang@google.com>
I have just encountered a kernel panic with this patch. Will submit a new
version after working on it.
Thanks,
Joonwon Kang
prev parent reply other threads:[~2026-04-08 11:04 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-08 10:06 Joonwon Kang
2026-04-08 11:04 ` Joonwon Kang [this message]
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