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

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Message-ID: <ZUNOTRWCWNJkn66n@gpd>
Date:   Thu, 2 Nov 2023 08:22:53 +0100
From:   Andrea Righi <andrea.righi@...onical.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Luis Chamberlain <mcgrof@...nel.org>,
        linux-modules@...r.kernel.org, patches@...ts.linux.dev,
        linux-kernel@...r.kernel.org, keescook@...omium.org,
        zhumao001@...suo.com, yangtiezhu@...ngson.cn, ojeda@...nel.org
Subject: Re: [GIT PULL] Modules changes for v6.7-rc1

On Wed, Nov 01, 2023 at 09:02:51PM -1000, Linus Torvalds wrote:
> 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

I proposed that change mostlfy for consistency with the zstd case, but I
haven't experience any issue with gzip compressed modules (that seem to
require less memory, even with larger modules).

So, yes, it probably makes sense to drop this change for now and I can
send another patch to switch to kvmalloc() for all the decompress cases.

Thanks,
-Andrea