Message-ID: <56c0671c-6db2-05ac-66a0-6f24101e6c5a@suse.cz>
Date:   Mon, 22 Nov 2021 12:49:35 +0100
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To:     Christoph Lameter <cl@gentwo.org>
Cc:     Rustam Kovhaev <rkovhaev@gmail.com>, penberg@kernel.org,
        rientjes@google.com, iamjoonsoo.kim@lge.com,
        akpm@linux-foundation.org, corbet@lwn.net, djwong@kernel.org,
        david@fromorbit.com, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, linux-doc@vger.kernel.org,
        gregkh@linuxfoundation.org, viro@zeniv.linux.org.uk,
        dvyukov@google.com
References: <037227db-c869-7d9c-65e8-8f5f8682171d@suse.cz>
 <20211122013026.909933-1-rkovhaev@gmail.com>
 <alpine.DEB.2.22.394.2111221018070.202803@gentwo.de>
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 <alpine.DEB.2.22.394.2111221133110.204314@gentwo.de>
 <148d2774-77b9-bb25-c132-80b00e16ea06@suse.cz>
 <alpine.DEB.2.22.394.2111221239050.205511@gentwo.de>
From:   Vlastimil Babka <vbabka@suse.cz>
Subject: Re: [PATCH v4] slob: add size header to all allocations
In-Reply-To: <alpine.DEB.2.22.394.2111221239050.205511@gentwo.de>
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On 11/22/21 12:40, Christoph Lameter wrote:
> On Mon, 22 Nov 2021, Vlastimil Babka wrote:
> 
>> It's no problem to have the real beginning of the object aligned, and the
>> prepended header not. The code already does that before this patch for the
>> kmalloc power-of-two alignments, where e.g. the object can be aligned to 256
>> bytes, but the prepended header to a smaller ARCH_KMALLOC_MINALIGN /
>> ARCH_SLAB_MINALIGN.
> 
> Ok but then the first object in a page may still have those issues.

Hmm, that's right. I guess we should also distinguish ARCH_KMALLOC_MINALIGN
for kmalloc paths, and ARCH_SLAB_MINALIGN for kmem_cache_alloc paths. Seems
the latter is generally smaller, thus some holes left by kmalloc allocations
could be filled later by kmem_cache_alloc allocations.

> 
>> > I dont know but it seems that making slob that sophisticated is counter
>> > productive. Remove SLOB?
>>
>> I wouldn't mind, but somebody might :)
> 
> Well run a space efficiency analysis after this patch. If the memory used
> is larger than SLUB (with the configuration for minimal data footprint)
> then there is no reason for SLOB to continue.

Makes sense.