linux-kernel - Re: [PATCH v3 1/7] mm, slab: combine kmalloc_caches and kmalloc_dma

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Date:   Fri, 20 Jul 2018 11:30:23 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Mel Gorman <mgorman@...hsingularity.net>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
        Roman Gushchin <guro@...com>, Michal Hocko <mhocko@...nel.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Christoph Lameter <cl@...ux.com>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Matthew Wilcox <willy@...radead.org>,
        "Luis R. Rodriguez" <mcgrof@...nel.org>
Subject: Re: [PATCH v3 1/7] mm, slab: combine kmalloc_caches and
 kmalloc_dma_caches

On 07/19/2018 10:10 AM, Mel Gorman wrote:
> On Wed, Jul 18, 2018 at 03:36:14PM +0200, Vlastimil Babka wrote:
>> The kmalloc caches currently mainain separate (optional) array
>> kmalloc_dma_caches for __GFP_DMA allocations. There are tests for __GFP_DMA in
>> the allocation hotpaths. We can avoid the branches by combining kmalloc_caches
>> and kmalloc_dma_caches into a single two-dimensional array where the outer
>> dimension is cache "type". This will also allow to add kmalloc-reclaimable
>> caches as a third type.
>>
>> Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
> 
> I'm surprised there are so many kmalloc users that require the DMA zone.
> Some of them are certainly bogus such as in drivers for archs that only
> have one zone and is probably a reflection of the confusing naming. The
> audit would be a mess and unrelated to the patch so for this patch;

Yeah, there was a session about that on LSF/MM and Luis was working on
it. One of the motivations was to get rid of the branch, so that's
sidestepped by this patch. I would still like to not have slabinfo full
of empty dma-kmalloc caches though :)

> Acked-by: Mel Gorman <mgorman@...hsingularity.net>
>