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Date: Tue, 17 Apr 2018 09:40:15 -0500 (CDT)
From: Christopher Lameter <cl@linux.com>
Subject: Re: slab: introduce the flag SLAB_MINIMIZE_WASTE
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To: Mikulas Patocka <mpatocka@redhat.com>
Cc: Vlastimil Babka <vbabka@suse.cz>, Mike Snitzer <snitzer@redhat.com>, Matthew Wilcox <willy@infradead.org>, Pekka Enberg <penberg@kernel.org>, linux-mm@kvack.org, dm-devel@redhat.com, David Rientjes <rientjes@google.com>, Joonsoo Kim <iamjoonsoo.kim@lge.com>, Andrew Morton <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org

On Mon, 16 Apr 2018, Mikulas Patocka wrote:

> dm-bufio deals gracefully with allocation failure, because it preallocates
> some buffers with vmalloc, but other subsystems may not deal with it and
> they cound return ENOMEM randomly or misbehave in other ways. So, the
> "SLAB_MINIMIZE_WASTE" flag is also saying that the allocation may fail and
> the caller is prepared to deal with it.
>
> The slub subsystem does actual fallback to low-order when the allocation
> fails (it allows different order for each slab in the same cache), but
> slab doesn't fallback and you get NULL if higher-order allocation fails.
> So, SLAB_MINIMIZE_WASTE is needed for slab because it will just randomly
> fail with higher order.

Fix Slab instead of adding a flag that is only useful for one allocator?