linux-kernel - Re: [PATCH 2/4] mm/slub: allow to set node and align in k[v]realloc

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Message-ID: <aF6DmPmeSpWU3hH_@pc636>
Date: Fri, 27 Jun 2025 13:42:16 +0200
From: Uladzislau Rezki <urezki@...il.com>
To: Danilo Krummrich <dakr@...nel.org>,
	Vitaly Wool <vitaly.wool@...sulko.se>
Cc: Vitaly Wool <vitaly.wool@...sulko.se>, linux-mm@...ck.org,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	Uladzislau Rezki <urezki@...il.com>,
	Alice Ryhl <aliceryhl@...gle.com>, rust-for-linux@...r.kernel.org
Subject: Re: [PATCH 2/4] mm/slub: allow to set node and align in k[v]realloc

Hello, Vitaly, Danilo.

> On Fri, Jun 27, 2025 at 11:37:14AM +0200, Vitaly Wool wrote:
> > Reimplement k[v]realloc_node() to be able to set node and
> > alignment should a user need to do so. In order to do that while
> > retaining the maximal backward compatibility, the following rules
> > are honored:
> > * kmalloc/kzalloc/krealloc remain unchanged
> > * kvmalloc/kvrealloc/kvcalloc remain unchanged
> > * kvrealloc remains unchanged
> > * kvrealloc_node is implemented as a new function taking align and
> >   NUMA id as extra parameters compared to kvrealloc.
> > * krealloc_node is implemented as a new function taking NUMA id
> >   as an extra parameter compared to krealloc
> > * kvmalloc_node/kvzalloc_node/kvcalloc_node get an extra parameter
> >   (alignment)
> 
> I see what you're doing here:
> 
> You created vrealloc_node_noprof() in the previous patch, taking the following
> arguments:
> 
> 	vrealloc_node_noprof(const void *p, size_t size,
> 			     unsigned long align,
> 			     gfp_t flags, int nid)
> 
> And now you're aligning the newly introduced krealloc_node() and
> kvrealloc_node() with that.
> 
> The idea for having an align argument on krealloc_node() simply is that it
> fails if the alignment requirement can't be fulfilled by the corresponding
> kmalloc bucket, such that we can fall back to vrealloc_node() in
> kvrealloc_node().
> 
> Generally, this makes sense to me.
> 
> However, now you consequently have to add the align argument to kvmalloc_node(),
> kvzalloc_node(), kvcalloc_node() as well.
> 
> This is what creates this huge diffstat changing all the users.
> 
> IMHO, the problem here was introduced already with vrealloc_node_noprof() taking
> an align argument in your previous patch, since now you have to adjust
> everything else to logically follow the same naming scheme.
> 
> Instead, I think you should introduce vrealloc_node_align(),
>
I am probably missing something. Could you please clarify why do you
need the vrealloc_node_align() and other friends? Do you have users
which require vrealloc() or kvrealloc() to support nid and align from
Rust API point of view? 

Thank you in advance!

--
Uladzislau Rezki