From: Andrew Morton <akpm@linux-foundation.org>
To: Joonwon Kang <joonwonkang@google.com>
Cc: dennis@kernel.org, tj@kernel.org, cl@gentwo.org,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] percpu: Fix hint invariant breakage
Date: Fri, 20 Mar 2026 12:08:48 -0700 [thread overview]
Message-ID: <20260320120848.ba7ddc21aaa4edab8c2b5b58@linux-foundation.org> (raw)
In-Reply-To: <20260320115214.143933-1-joonwonkang@google.com>
On Fri, 20 Mar 2026 11:52:14 +0000 Joonwon Kang <joonwonkang@google.com> wrote:
> 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 it.
>
> - if (new contig == contig_hint > scan_hint) && (start <
> contig_hint_start) && the new contig is not to become a new
> contig_hint, then scan_hint should be invalidated instead of being
> updated to the new contig.
>
> This commit fixes this invariant breakage and also optimizes scan_hint
> by keeping it or updating it when acceptable:
>
> - 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.
>
Thanks. Does the change have any observable runtime effects?
Was this patch inspired by code inspection?
next prev parent reply other threads:[~2026-03-20 19:08 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-03-20 11:52 [PATCH] percpu: Fix hint invariant breakage Joonwon Kang
2026-03-20 19:08 ` Andrew Morton [this message]
2026-03-23 12:02 ` Joonwon Kang
2026-03-21 17:09 ` Dennis Zhou
2026-03-23 14:05 ` Joonwon Kang
2026-04-09 18:09 ` Dennis Zhou
2026-04-20 12:35 ` Joonwon Kang
2026-04-22 0:12 ` Dennis Zhou
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20260320120848.ba7ddc21aaa4edab8c2b5b58@linux-foundation.org \
--to=akpm@linux-foundation.org \
--cc=cl@gentwo.org \
--cc=dennis@kernel.org \
--cc=joonwonkang@google.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=tj@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.