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Date: Fri, 7 Nov 2025 13:06:37 +0100
From: Christoph Hellwig <hch@lst.de>
To: Eric Biggers <ebiggers@kernel.org>
Cc: Christoph Hellwig <hch@lst.de>, Jens Axboe <axboe@kernel.dk>,
	Vlastimil Babka <vbabka@suse.cz>,
	Andrew Morton <akpm@linux-foundation.org>,
	Christoph Lameter <cl@gentwo.org>,
	David Rientjes <rientjes@google.com>,
	Roman Gushchin <roman.gushchin@linux.dev>,
	Harry Yoo <harry.yoo@oracle.com>, linux-block@vger.kernel.org,
	linux-fsdevel@vger.kernel.org, linux-fscrypt@vger.kernel.org,
	linux-mm@kvack.org
Subject: Re: [PATCH 3/9] mempool: add mempool_{alloc,free}_bulk
Message-ID: <20251107120637.GC30551@lst.de>
References: <20251031093517.1603379-1-hch@lst.de> <20251031093517.1603379-4-hch@lst.de> <20251107035207.GA47797@sol>
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User-Agent: Mutt/1.5.17 (2007-11-01)

On Thu, Nov 06, 2025 at 07:52:07PM -0800, Eric Biggers wrote:
> > +int mempool_alloc_bulk_noprof(struct mempool *pool, void **elem,
> > +		unsigned int count, gfp_t gfp_mask, unsigned long caller_ip)
> 
> What exactly is the behavior on partial failures?  Is the return value 0
> or is it -ENOMEM, and is the array restored to its original state or
> might some elements have been allocated?

Right now it frees everything.  But as per the discussion with Vlastimil
I'll move to not allowing non-blocking allocations for multiple elements,
at which point the failure case just can't happen and that is sorted out.

> > +}
> >  EXPORT_SYMBOL(mempool_alloc_noprof);
> 
> How much overhead does this add to mempool_alloc(), which will continue
> to be the common case?  I wonder if it would be worthwhile to
> force-inline the bulk allocation function into it, so that it will get
> generate about the same code as before.

It's about 10 extra instructions looking at my profiles.  So I don't
think it matters, but if the maintainers prefer force inlining I
can do that.