linux-kernel - Re: [PATCH] mm: kmalloc_index: remove case when size is more than 32MB

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAB=+i9QyxOu_1QDfX5QA=pOxxnRURPnwd2Y0EbhoO1u0e=irBA@mail.gmail.com>
Date:   Sun, 9 May 2021 14:33:38 +0900
From:   Hyeonggon Yoo <42.hyeyoo@...il.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     cl@...ux.com, penberg@...nel.org, rientjes@...gle.com,
        iamjoonsoo.kim@....com, vbabka@...e.cz, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: kmalloc_index: remove case when size is more than 32MB

On Sun, May 09, 2021 at 12:19:40AM +0100, Matthew Wilcox wrote:
> On Sun, May 09, 2021 at 07:13:28AM +0900, Hyeonggon Yoo wrote:
> > the return value of kmalloc_index is used as index of kmalloc_caches,
>
> it doesn't matter.  every few weeks somebody posts a patch to "optimise"
> kmalloc_index, failing to appreciate that it's only ever run at compile
> time because it's all under __builtin_constant_p().

Oh thanks, I didn't know about __builtin_constant_p.

But I was not optimizing kmalloc_index. isn't it confusing that
kmalloc_caches alllows maximum size of 32MB, and kmalloc_index allows
maximum size of 64MB?

and even if the code I removed is never reached because 64MB is always
bigger than KMALLOC_MAX_CACHE_SIZE, it will cause an error if reached.