linux-kernel - Re: [PATCH v3 5/5] mm/slub: do not create dma-kmalloc if no managed pages in DMA zone

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Date:   Tue, 14 Dec 2021 11:28:01 +0100 (CET)
From:   Christoph Lameter <cl@...two.org>
To:     Vlastimil Babka <vbabka@...e.cz>
cc:     Baoquan He <bhe@...hat.com>, Hyeonggon Yoo <42.hyeyoo@...il.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        akpm@...ux-foundation.org, hch@....de, John.p.donnelly@...cle.com,
        kexec@...ts.infradead.org, stable@...r.kernel.org,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH v3 5/5] mm/slub: do not create dma-kmalloc if no managed
 pages in DMA zone

On Tue, 14 Dec 2021, Vlastimil Babka wrote:

> If doesn't feel right to me to fix (or rather workaround) this on the level
> of kmalloc caches just because the current reports come from there. If we
> decide it's acceptable for kdump kernel to return !ZONE_DMA memory for
> GFP_DMA requests, then it should apply at the page allocator level for all
> allocations, not just kmalloc().
>
> Also you mention above you'd prefer ZONE_DMA32 memory, while chances are
> this approach of using KMALLOC_NORMAL caches will end up giving you
> ZONE_NORMAL. On the page allocator level it would be much easier to
> implement a fallback from non-populated ZONE_DMA to ZONE_DMA32 specifically.

Well this only works if the restrictions on the physical memory addresses
of each platform make that possible.