linux-kernel - Re: [PATCH v3] slob: add size header to all allocations

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Date:   Tue, 16 Nov 2021 12:26:17 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Rustam Kovhaev <rkovhaev@...il.com>, cl@...ux.com,
        penberg@...nel.org, rientjes@...gle.com, iamjoonsoo.kim@....com,
        akpm@...ux-foundation.org, corbet@....net
Cc:     djwong@...nel.org, david@...morbit.com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-doc@...r.kernel.org, gregkh@...uxfoundation.org,
        viro@...iv.linux.org.uk, dvyukov@...gle.com
Subject: Re: [PATCH v3] slob: add size header to all allocations

On 10/29/21 05:05, Rustam Kovhaev wrote:
> Let's prepend both kmalloc() and kmem_cache_alloc() allocations with the
> size header.
> It simplifies the slab API and guarantees that both kmem_cache_alloc()
> and kmalloc() memory could be freed by kfree().
> 
> meminfo right after the system boot, x86-64 on xfs, without the patch:
> Slab:              35456 kB
> 
> the same, with the patch:
> Slab:              36100 kB
> 
> Link: https://lore.kernel.org/lkml/20210929212347.1139666-1-rkovhaev@gmail.com
> Signed-off-by: Rustam Kovhaev <rkovhaev@...il.com>

Sorry for the late reply. I think we can further simplify this. We have:

static void *slob_alloc(size_t size, gfp_t gfp, int align,
			int node, int align_offset)

Previously there was one caller that passed size as unchanged, align_offset
= 0, the other passed size + SLOB_HDR_SIZE, align_offset = SLOB_HDR_SIZE.
Now both callers do the latter. We can drop the align_offset parameter and
pass size unchanged. slob_alloc() can internally add SLOB_HDR_SIZE to size,
and use SLOB_HDR_SIZE instead of align_offset.

Thanks,
Vlastimil