From: Wilco Dijkstra <Wilco.Dijkstra@arm.com>
To: Florian Weimer <fweimer@redhat.com>, DJ Delorie <dj@redhat.com>
Cc: "libc-alpha@sourceware.org" <libc-alpha@sourceware.org>
Subject: Re: [PATCH] malloc: Use correct C11 atomics for fastbin
Date: Fri, 2 Dec 2022 10:56:30 +0000 [thread overview]
Message-ID: <PAWPR08MB8982C8C13946E71A8C68290B83179@PAWPR08MB8982.eurprd08.prod.outlook.com> (raw)
In-Reply-To: <87sfhytir0.fsf@oldenburg.str.redhat.com>
Hi,
>> Wilco Dijkstra via Libc-alpha <libc-alpha@sourceware.org> writes:
>>> +/* Atomically pop from the fastbin list. The arena lock must be held to
>>> + block other threads removing entries, avoiding the ABA issue. */
>>
>> If the arena lock must be held anyway, why go through the compare and
>> exchange overhead? We know we're the only thread accessing it.
>
> Other threads are adding entries without the arena lock.
Yes, malloc is blocking but free isn't and accesses the freelist concurrently.
It's a really weird design. Splitting the free list into a local one and a shared
one would be far better - no atomics when you have the malloc lock, and if
the local free list is empty it takes one atomic to copy all shared entries.
Cheers,
Wilco
next prev parent reply other threads:[~2022-12-02 10:56 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-11-21 16:09 Wilco Dijkstra
2022-11-21 16:18 ` Florian Weimer
2022-11-21 16:55 ` Wilco Dijkstra
2022-11-21 16:56 ` Wilco Dijkstra
2022-11-21 17:00 ` Florian Weimer
2022-12-02 5:11 ` DJ Delorie
2022-12-02 6:36 ` Florian Weimer
2022-12-02 10:56 ` Wilco Dijkstra [this message]
2022-12-02 11:24 ` Florian Weimer
2022-12-02 12:02 ` Wilco Dijkstra
2022-12-02 18:55 ` DJ Delorie
2022-12-05 18:39 ` Zack Weinberg
2022-12-06 16:19 ` DJ Delorie
2022-12-12 3:35 ` Zack Weinberg
2022-12-12 11:57 ` Florian Weimer
2022-12-12 11:56 ` Florian Weimer
2022-12-06 13:29 ` Wilco Dijkstra
2022-12-06 13:37 ` Adhemerval Zanella Netto
2022-12-06 14:31 ` Zack Weinberg
2022-12-06 16:23 ` DJ Delorie
2022-12-15 15:43 ` Wilco Dijkstra
2022-12-02 18:55 ` DJ Delorie
2022-12-06 15:04 Wilco Dijkstra
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=PAWPR08MB8982C8C13946E71A8C68290B83179@PAWPR08MB8982.eurprd08.prod.outlook.com \
--to=wilco.dijkstra@arm.com \
--cc=dj@redhat.com \
--cc=fweimer@redhat.com \
--cc=libc-alpha@sourceware.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 a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).