From: Eric Biggers <ebiggers@kernel.org>
To: Christoph Hellwig <hch@infradead.org>
Cc: linux-block@vger.kernel.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org, Jens Axboe <axboe@kernel.dk>,
Vlastimil Babka <vbabka@kernel.org>, Harry Yoo <harry@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Hao Li <hao.li@linux.dev>, Christoph Lameter <cl@gentwo.org>,
David Rientjes <rientjes@google.com>,
Roman Gushchin <roman.gushchin@linux.dev>
Subject: Re: [PATCH 2/3] mm: support fallible mempool_alloc_bulk()
Date: Tue, 11 Aug 2026 14:03:38 -0700 [thread overview]
Message-ID: <20260811210338.GB1905@sol> (raw)
In-Reply-To: <anuCcb-Cma6JOAb0@infradead.org>
On Tue, Aug 11, 2026 at 01:13:37PM -0700, Christoph Hellwig wrote:
> What is actually efficient is do skip the mempool entirely from the
> original submission context and do a non-mempool GFP_NOIO allocation,
> and only in the extremely unlikely case that this fails fall back to
> the rescruer thread.
It definitely is *not* more efficient to fall back to a kworker for a
small task (removing elements from a mempool that has them available)
that could just be done synchronously. Scheduling overhead is a huge
problem for kernel features doing I/O pre or post-processing. The idea
that scheduling a kworker is lightweight compared to the actual I/O is
quite outdated.
Sure, this case triggers only when the regular allocations fail anyway.
So it shouldn't be a big deal, and I'll send a patch that implements it
the less efficient way that you prefer. But it's a little unfortunate
that you're not going to allow it to be implemented properly.
- Eric
next prev parent reply other threads:[~2026-08-11 21:05 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-08-06 22:10 [PATCH 0/3] Fix a deadlock in blk-crypto-fallback Eric Biggers
2026-08-06 22:10 ` [PATCH 1/3] mm: make mempool_alloc_from_pool() return bool Eric Biggers
2026-08-10 15:59 ` Christoph Hellwig
2026-08-06 22:10 ` [PATCH 2/3] mm: support fallible mempool_alloc_bulk() Eric Biggers
2026-08-10 16:00 ` Christoph Hellwig
2026-08-10 16:14 ` Eric Biggers
2026-08-10 17:21 ` Christoph Hellwig
2026-08-10 18:22 ` Eric Biggers
2026-08-11 20:13 ` Christoph Hellwig
2026-08-11 21:03 ` Eric Biggers [this message]
2026-08-06 22:10 ` [PATCH 3/3] blk-crypto-fallback: Fix deadlock when encrypting large bio in dm layer Eric Biggers
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