Re: [PATCH 7/8] readahead: basic support for backwards prefetching

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On Mon, Nov 21, 2011 at 03:33:09PM -0800, Andrew Morton wrote:
> On Mon, 21 Nov 2011 17:18:26 +0800
> Wu Fengguang <fengguang.wu@xxxxxxxxx> wrote:
> 
> > Add the backwards prefetching feature. It's pretty simple if we don't
> > support async prefetching and interleaved reads.
> 
> Well OK, but I wonder how many applications out there read files in
> reverse order.  Is it common enough to bother special-casing in the
> kernel like this?

Maybe not so many applications, but sure there are some real cases
somewhere. I remember an IBM paper (that's many years ago, so cannot
recall the exact title) on database shows a graph containing backwards
reading curves among the other ones.

Recently Shaohua even run into a performance regression caused by glibc
optimizing memcpy to access page in reverse order (15, 14, 13, ... 0).

Well this patch may not be the most pertinent fix to that particular
issue. But you see the opportunity such access patterns arise from
surprised areas. 

Thanks,
Fengguang
--
To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html


[Index of Archives]     [Linux Ext4 Filesystem]     [Union Filesystem]     [Filesystem Testing]     [Ceph Users]     [Ecryptfs]     [AutoFS]     [Kernel Newbies]     [Share Photos]     [Security]     [Netfilter]     [Bugtraq]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux Cachefs]     [Reiser Filesystem]     [Linux RAID]     [Samba]     [Device Mapper]     [CEPH Development]
  Powered by Linux