linux-kernel - Re: [PATCH] mm/filemap: Implement fast short reads

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Message-ID: <CAHk-=wigaATtHqwU+KHRzf-t2jGmD=zT3tGnJVD+4MAk86tpNg@mail.gmail.com>
Date: Tue, 21 Oct 2025 05:50:19 -1000
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Kiryl Shutsemau <kirill@...temov.name>
Cc: Andrew Morton <akpm@...ux-foundation.org>, David Hildenbrand <david@...hat.com>, 
	Matthew Wilcox <willy@...radead.org>, Alexander Viro <viro@...iv.linux.org.uk>, 
	Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>, linux-mm@...ck.org, 
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Suren Baghdasaryan <surenb@...gle.com>
Subject: Re: [PATCH] mm/filemap: Implement fast short reads

On Mon, 20 Oct 2025 at 01:33, Kiryl Shutsemau <kirill@...temov.name> wrote:
>
> On Sun, Oct 19, 2025 at 09:53:28PM -0700, Andrew Morton wrote:
> >
> > A use case for alloca() or equiv.  That would improve the average-case
> > stack depth but not the worst-case.
>
> __kstack_alloca()/__builtin_alloca() would work and it bypassed
> -Wframe-larger-than warning.
>
> But I don't see any real users.

Yes, and we've walked away from alloca() (and on-stack VLAs, which are
really exactly the same thing as far as a compiler is concerned),
because it makes static analysis much *MUCH* harder.

Let's not ever re-introduce dynamic stack use in the kernel.

                Linus