linux-kernel - Re: [PATCH 1/2] mm: vmalloc: implement vrealloc()

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Message-ID: <ZpiJDdqhDlAb8n6T@infradead.org>
Date: Wed, 17 Jul 2024 20:16:29 -0700
From: Christoph Hellwig <hch@...radead.org>
To: Danilo Krummrich <dakr@...nel.org>
Cc: cl@...ux.com, penberg@...nel.org, rientjes@...gle.com,
	iamjoonsoo.kim@....com, akpm@...ux-foundation.org, vbabka@...e.cz,
	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,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	rust-for-linux@...r.kernel.org
Subject: Re: [PATCH 1/2] mm: vmalloc: implement vrealloc()

On Thu, Jul 18, 2024 at 12:24:01AM +0200, Danilo Krummrich wrote:
> +extern void * __must_check vrealloc_noprof(const void *p, size_t size,
> +					   gfp_t flags) __realloc_size(2);

No need for the extern here.

It would also help readability a bit to keep the __realloc_size on a
separate like, aka:

void *__must_check vrealloc_noprof(const void *p, size_t size, gfp_t flags)
		__realloc_size(2);

> +	if (size <= old_size) {
> +		/* TODO: Can we optimize and shrink the allocation? What would
> +		 * be a good metric for when to shrink the vm_area?
> +		 */

Kernel comment style is to keep the

		/*

on a line of it's own.  A realloc that doesn't shrink is a bit
pointless.  The same heuristics as for krealloc should probably apply
here, adjust to the fact that we always deal with whole pages.


> +	/* TODO: Can we optimize and extend the existing allocation if we have
> +	 * enough contiguous space left in the virtual address space?
> +	 */

I don't understand this comment.

> +EXPORT_SYMBOL(vrealloc_noprof);

New interfaces should be EXPORT_SYMBOL_GPL.  That being said for this
to be added an exported we'll need an actual user to start with anyway.