linux-kernel - Re: [PATCH v3 0/2] iov_iter: allow iov_iter_get_pages

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Date:   Thu, 2 Feb 2017 23:49:01 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     Jeff Layton <jlayton@...hat.com>
Cc:     Al Viro <viro@...IV.linux.org.uk>,
        Christoph Hellwig <hch@...radead.org>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-nfs@...r.kernel.org, ceph-devel@...r.kernel.org,
        lustre-devel@...ts.lustre.org,
        v9fs-developer@...ts.sourceforge.net,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jan Kara <jack@...e.cz>,
        Chris Wilson <chris@...is-wilson.co.uk>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH v3 0/2] iov_iter: allow iov_iter_get_pages_alloc to
 allocate more pages per call

On Thu, Feb 02, 2017 at 08:00:52AM -0500, Jeff Layton wrote:
> Yeah, that might work. You could kmalloc the buffer array according to
> the maxsize value. For small ones we could even consider using an on-
> stack buffer.

For the block direct I/O code we defintively want to avoid any
allocations for small I/O a that shows up in the performance numbers.
And we'd like to reuse the on-stack bio_vec so that the defintion of
a small I/O can be as big as possible without blowing up the stack.