From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoph Hellwig Subject: Re: [PATCH] remap_file_pages.2: Not actually useful on real files. Date: Thu, 8 May 2014 05:50:32 -0700 Message-ID: <20140508125032.GA24087@infradead.org> References: <5de30c3a21531919712fc7df213c18b46e521225.1355955125.git.luto@amacapital.net> <536B5221.60407@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Andy Lutomirski , linux-man-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: "Michael Kerrisk (man-pages)" Return-path: Content-Disposition: inline In-Reply-To: <536B5221.60407-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> Sender: linux-man-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-fsdevel.vger.kernel.org On Thu, May 08, 2014 at 11:45:05AM +0200, Michael Kerrisk (man-pages) wrote: > I've applied the above. I then tweaked it a little. Is the following > okay: > > [[ > Since Linux 2.6.23, > .\" commit 3ee6dafc677a68e461a7ddafc94a580ebab80735 > .BR remap_file_pages () > has no performance advantage over > .BR mmap (2) > when used on real files: > on real files it creates a separate VMA for each range. > It does, however, continue to provide a performance advantage > for files on memory-based filesystems. > ]] I think "real file" is a very bad term. What is more real about one file vs another? Is NFS less real than XFS, is tmpfs more real than ramfs? I'd reword this more like this: Since Linux 2.6.23, remap_file_pages only creates non-linear mappings on in-memory file systems like tmpfs, hugetlbfs or ramfs. File systems with a backing store provide a less efficient emulation. I think the whole man page for remap_file_pages is a litt confusing I have to say, the concept of a VMA is purely kernel internal and doesn't really have a meaning for applications and thus shouldn't appear in a man page. While we're at it: It seems like we should get rid of the remap_pages vma operation - it's set by lots of filesystems that can never have it invoked, and always is set to generic_file_remap_pages anyway. -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html