Re: [PATCH 02/11] mm: call import_iovec() instead of rw_copy_check_uvector() in process_vm_rw()

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To: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Subject: Re: [PATCH 02/11] mm: call import_iovec() instead of rw_copy_check_uvector() in process_vm_rw()
From: Christoph Hellwig <hch@xxxxxx>
Date: Mon, 21 Sep 2020 18:12:24 +0200
Cc: David Laight <David.Laight@xxxxxxxxxx>, Christoph Hellwig <hch@xxxxxx>, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>, Jens Axboe <axboe@xxxxxxxxx>, Arnd Bergmann <arnd@xxxxxxxx>, David Howells <dhowells@xxxxxxxxxx>, "linux-arm-kernel@xxxxxxxxxxxxxxxxxxx" <linux-arm-kernel@xxxxxxxxxxxxxxxxxxx>, "linux-kernel@xxxxxxxxxxxxxxx" <linux-kernel@xxxxxxxxxxxxxxx>, "linux-mips@xxxxxxxxxxxxxxx" <linux-mips@xxxxxxxxxxxxxxx>, "linux-parisc@xxxxxxxxxxxxxxx" <linux-parisc@xxxxxxxxxxxxxxx>, "linuxppc-dev@xxxxxxxxxxxxxxxx" <linuxppc-dev@xxxxxxxxxxxxxxxx>, "linux-s390@xxxxxxxxxxxxxxx" <linux-s390@xxxxxxxxxxxxxxx>, "sparclinux@xxxxxxxxxxxxxxx" <sparclinux@xxxxxxxxxxxxxxx>, "linux-block@xxxxxxxxxxxxxxx" <linux-block@xxxxxxxxxxxxxxx>, "linux-scsi@xxxxxxxxxxxxxxx" <linux-scsi@xxxxxxxxxxxxxxx>, "linux-fsdevel@xxxxxxxxxxxxxxx" <linux-fsdevel@xxxxxxxxxxxxxxx>, "linux-aio@xxxxxxxxx" <linux-aio@xxxxxxxxx>, "io-uring@xxxxxxxxxxxxxxx" <io-uring@xxxxxxxxxxxxxxx>, "linux-arch@xxxxxxxxxxxxxxx" <linux-arch@xxxxxxxxxxxxxxx>, "linux-mm@xxxxxxxxx" <linux-mm@xxxxxxxxx>, "netdev@xxxxxxxxxxxxxxx" <netdev@xxxxxxxxxxxxxxx>, "keyrings@xxxxxxxxxxxxxxx" <keyrings@xxxxxxxxxxxxxxx>, "linux-security-module@xxxxxxxxxxxxxxx" <linux-security-module@xxxxxxxxxxxxxxx>
In-reply-to: <20200921152937.GX3421308@ZenIV.linux.org.uk>
User-agent: Mutt/1.5.17 (2007-11-01)

On Mon, Sep 21, 2020 at 04:29:37PM +0100, Al Viro wrote:
> On Mon, Sep 21, 2020 at 03:21:35PM +0000, David Laight wrote:
> 
> > You really don't want to be looping through the array twice.
> 
> Profiles, please.

Given that the iov array should be cache hot I'd be surprised to
see a huge difference.

References:
- let import_iovec deal with compat_iovecs as well v2
  - From: Christoph Hellwig
- [PATCH 02/11] mm: call import_iovec() instead of rw_copy_check_uvector() in process_vm_rw()
  - From: Christoph Hellwig
- Re: [PATCH 02/11] mm: call import_iovec() instead of rw_copy_check_uvector() in process_vm_rw()
  - From: Al Viro
- RE: [PATCH 02/11] mm: call import_iovec() instead of rw_copy_check_uvector() in process_vm_rw()
  - From: David Laight
- Re: [PATCH 02/11] mm: call import_iovec() instead of rw_copy_check_uvector() in process_vm_rw()
  - From: Al Viro

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