linux-kernel - Re: [GIT PULL] Modules changes for v6.7-rc1

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Message-ID: <CAHk-=whFXNYXG2ES8HdoaMC=O4bakMXGZezmoqA3SXwn4xJUPQ@mail.gmail.com>
Date:   Wed, 1 Nov 2023 21:02:51 -1000
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Luis Chamberlain <mcgrof@...nel.org>
Cc:     linux-modules@...r.kernel.org, patches@...ts.linux.dev,
        linux-kernel@...r.kernel.org, andrea.righi@...onical.com,
        keescook@...omium.org, zhumao001@...suo.com,
        yangtiezhu@...ngson.cn, ojeda@...nel.org
Subject: Re: [GIT PULL] Modules changes for v6.7-rc1

On Wed, 1 Nov 2023 at 10:13, Luis Chamberlain <mcgrof@...nel.org> wrote:
>
> The only thing worth highligthing is that gzip moves to use vmalloc() instead of
> kmalloc just as we had a fix for this for zstd on v6.6-rc1.

Actually, that's almost certainly entirely the wrong thing to do.

Unless you *know* that the allocation is large, you shouldn't use
vmalloc(). And since kmalloc() has worked fine, you most definitely
don't know that.

So we have 'kvmalloc()' *exactly* for this reason, which is a "use
kmalloc, unless that is too small, then use vmalloc".

kmalloc() isn't just about "use physically contiguous allocations".
It's also more memory-efficient, and a *lot* faster than vmalloc(),
which has to play VM tricks.

So this "just switch to vmalloc()" is entirely wrong.

              Linus