From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Tue, 2 Dec 2008 13:04:10 +0000 From: John Levon Subject: Re: [patch][rfc] fs: shrink struct dentry Message-ID: <20081202130410.GA24222@totally.trollied.org.uk> References: <20081201083343.GC2529@wotan.suse.de> <20081201175113.GA16828@totally.trollied.org.uk> <20081201180455.GJ10790@wotan.suse.de> <20081201193818.GB16828@totally.trollied.org.uk> <20081202070608.GA28080@wotan.suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20081202070608.GA28080@wotan.suse.de> Sender: owner-linux-mm@kvack.org Return-Path: To: Nick Piggin Cc: linux-fsdevel@vger.kernel.org, Linux Memory Management List , robert.richter@amd.com, oprofile-list@lists.sf.net List-ID: On Tue, Dec 02, 2008 at 08:06:08AM +0100, Nick Piggin wrote: > > Don't you even have a differential profile showing the impact of > > removing d_cookie? This hash table lookup will now happen on *every* > > userspace sample that's processed. That's, uh, a lot. > > I don't know what you mean by every sample that's processed, but > won't the hash lookup only happen for the *first* time that a given > name is asked for a dcookie (ie. fast_get_dcookie, which, as I said, > should actually be moved to fs/dcookies.c) I mis-read your changes. > > (By all means make your change, but I don't get how it's OK to regress > > other code, and provide no evidence at all as to its impact.) > > Tradeoffs are made all the time. This is obviously a good one, and ^^^^^^^^^^^^^^^^^^^^ By all means make your change, but I don't get how it's OK to regress other code, and provide no evidence at all as to its impact. > I provided evidence of the impact of the improvement in the common > case. I also acknowledge it can slow down the uncommon case, but > showed ways that can easily be improved. Do you want me to just try > to make an artificial case where I mmap thousands of tiny shared > libraries and try to overflow the hash and try to detect a difference? You haven't even bothered to show that it hasn't affected normal oprofile use yet. I can't believe I'm having to argue that you need to test your code. So I think I'll stop. > Did you add d_cookie? If so, then surely at the time you must have It was added along with the rest of oprofile, so I don't have breakout numbers. I did have oprofile overhead numbers, though I doubt I could find them now. john -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org