From: David Howells Subject: Re: Extended file stat: Splitting file- and fs-specific info? Date: Thu, 10 May 2012 10:14:11 +0100 Message-ID: <13791.1336641251@redhat.com> References: <20120509002420.GL5091@dastard> <20120419140558.17272.74360.stgit@warthog.procyon.org.uk> <16281.1336508382@redhat.com> Cc: dhowells-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, adilger-m1MBpc4rdrD3fQ9qLvQP4Q@public.gmane.org, bfields-uC3wQj2KruNg9hUCZPvPmw@public.gmane.org, smfrench-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, ben-/+tVBieCtBitmTQ+vhA3Yw@public.gmane.org, Trond.Myklebust-HgOvQuBEEgTQT0dZR+AlfA@public.gmane.org, roland-/Z5OmTQCD9xF6kxbq+BtvQ@public.gmane.org, linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-nfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-cifs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, samba-technical-w/Ol4Ecudpl8XjKLYN78aQ@public.gmane.org, linux-ext4-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, libc-alpha-9JcytcrH/bA+uJoB2kUjGw@public.gmane.org To: Dave Chinner Return-path: In-Reply-To: <20120509002420.GL5091@dastard> Sender: linux-cifs-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-ext4.vger.kernel.org Dave Chinner wrote: > > Also, do Dave Chinner's ideas for indicating five I/O parameters want to be > > 32-bit numbers? Larger? Smaller? Can they be log2? > > Definitely 32 bit, IMO, as it's not uncommon to see optimal IO sizes > in the tens of megabytes on large, high bandwidth storage systems. > As for being log2 - that's just making it more complex to use and > making code ugly - we'd have to convert to log2 in kernel, then > convert back in every single application.... ilog2() in the kernel uses the CPU's bit-scan instruction if it has one and converting back is just a bitshift operator. But let's go with 32-bit fields for the moment. I presume we aren't worried about a driver that wants to do a 4GB transfer... David