linux-kernel - Re: [PATCH v2 2/2] mm: kvmalloc: align kvrealloc() with krealloc()

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Message-ID: <6ff1f0d8-1483-49ce-a02a-3c4f3d664fa7@suse.cz>
Date: Fri, 26 Jul 2024 16:38:59 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: Danilo Krummrich <dakr@...nel.org>, cl@...ux.com, penberg@...nel.org,
 rientjes@...gle.com, iamjoonsoo.kim@....com, akpm@...ux-foundation.org,
 roman.gushchin@...ux.dev, 42.hyeyoo@...il.com, urezki@...il.com,
 hch@...radead.org, kees@...nel.org, ojeda@...nel.org, wedsonaf@...il.com,
 mhocko@...nel.org, mpe@...erman.id.au, chandan.babu@...cle.com,
 christian.koenig@....com, maz@...nel.org, oliver.upton@...ux.dev
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 rust-for-linux@...r.kernel.org
Subject: Re: [PATCH v2 2/2] mm: kvmalloc: align kvrealloc() with krealloc()

On 7/22/24 6:29 PM, Danilo Krummrich wrote:
> Besides the obvious (and desired) difference between krealloc() and
> kvrealloc(), there is some inconsistency in their function signatures
> and behavior:
> 
>  - krealloc() frees the memory when the requested size is zero, whereas
>    kvrealloc() simply returns a pointer to the existing allocation.
> 
>  - krealloc() behaves like kmalloc() if a NULL pointer is passed, whereas
>    kvrealloc() does not accept a NULL pointer at all and, if passed,
>    would fault instead.
> 
>  - krealloc() is self-contained, whereas kvrealloc() relies on the caller
>    to provide the size of the previous allocation.
> 
> Inconsistent behavior throughout allocation APIs is error prone, hence make
> kvrealloc() behave like krealloc(), which seems superior in all mentioned
> aspects.
> 
> Besides that, implementing kvrealloc() by making use of krealloc() and
> vrealloc() provides oppertunities to grow (and shrink) allocations more
> efficiently. For instance, vrealloc() can be optimized to allocate and
> map additional pages to grow the allocation or unmap and free unused
> pages to shrink the allocation.
> 
> Signed-off-by: Danilo Krummrich <dakr@...nel.org>

Acked-by: Vlastimil Babka <vbabka@...e.cz>

with same caveat about the __GFP_ZERO comment on kvrealloc_noprof()