linux-kernel - Re: [PATCH v2] mm/slab_common: move dma-kmalloc caches creation into new_kmalloc

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Date:   Tue, 12 Apr 2022 16:38:21 -0700 (PDT)
From:   David Rientjes <rientjes@...gle.com>
To:     Ohhoon Kwon <ohkwon1043@...il.com>
cc:     Hyeonggon Yoo <42.hyeyoo@...il.com>,
        Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        JaeSang Yoo <jsyoo5b@...il.com>,
        Wonhyuk Yang <vvghjk1234@...il.com>,
        Jiyoup Kim <lakroforce@...il.com>,
        Donghyeok Kim <dthex5d@...il.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] mm/slab_common: move dma-kmalloc caches creation into
 new_kmalloc_cache()

On Mon, 11 Apr 2022, Ohhoon Kwon wrote:

> There are four types of kmalloc_caches: KMALLOC_NORMAL, KMALLOC_CGROUP,
> KMALLOC_RECLAIM, and KMALLOC_DMA. While the first three types are
> created using new_kmalloc_cache(), KMALLOC_DMA caches are created in a
> separate logic. Let KMALLOC_DMA caches be also created using
> new_kmalloc_cache(), to enhance readability.
> 
> Historically, there were only KMALLOC_NORMAL caches and KMALLOC_DMA
> caches in the first place, and they were initialized in two separate
> logics. However, when KMALLOC_RECLAIM was introduced in v4.20 via
> commit 1291523f2c1d ("mm, slab/slub: introduce kmalloc-reclaimable
> caches") and KMALLOC_CGROUP was introduced in v5.14 via
> commit 494c1dfe855e ("mm: memcg/slab: create a new set of kmalloc-cg-<n>
> caches"), their creations were merged with KMALLOC_NORMAL's only.
> KMALLOC_DMA creation logic should be merged with them, too.
> 
> By merging KMALLOC_DMA initialization with other types, the following
> two changes might occur:
> 1. The order dma-kmalloc-<n> caches added in slab_cache list may be
> sorted by size. i.e. the order they appear in /proc/slabinfo may change
> as well.
> 2. slab_state will be set to UP after KMALLOC_DMA is created.
> In case of slub, freelist randomization is dependent on slab_state>=UP,
> and therefore KMALLOC_DMA cache's freelist will not be randomized in
> creation, but will be deferred to init_freelist_randomization().
> 
> Co-developed-by: JaeSang Yoo <jsyoo5b@...il.com>
> Signed-off-by: JaeSang Yoo <jsyoo5b@...il.com>
> Signed-off-by: Ohhoon Kwon <ohkwon1043@...il.com>

Acked-by: David Rientjes <rientjes@...gle.com>