linux-kernel - Re: [PATCH v4] slob: add size header to all allocations

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Message-ID: <alpine.DEB.2.22.394.2111221239050.205511@gentwo.de>
Date:   Mon, 22 Nov 2021 12:40:53 +0100 (CET)
From:   Christoph Lameter <cl@...two.org>
To:     Vlastimil Babka <vbabka@...e.cz>
cc:     Rustam Kovhaev <rkovhaev@...il.com>, penberg@...nel.org,
        rientjes@...gle.com, iamjoonsoo.kim@....com,
        akpm@...ux-foundation.org, corbet@....net, 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 v4] slob: add size header to all allocations

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.

> > 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.