From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail203.messagelabs.com (mail203.messagelabs.com [216.82.254.243]) by kanga.kvack.org (Postfix) with ESMTP id DF15A6B004F for ; Fri, 6 Feb 2009 07:33:53 -0500 (EST) Date: Fri, 6 Feb 2009 12:33:22 +0000 (GMT) From: Hugh Dickins Subject: Re: [patch] SLQB slab allocator In-Reply-To: <1233910649.29891.26.camel@penberg-laptop> Message-ID: References: <20090121143008.GV24891@wotan.suse.de> <84144f020901220201g6bdc2d5maf3395fc8b21fe67@mail.gmail.com> <1233545923.2604.60.camel@ymzhang> <1233565214.17835.13.camel@penberg-laptop> <1233646145.2604.137.camel@ymzhang> <1233714090.2604.186.camel@ymzhang> <1233910649.29891.26.camel@penberg-laptop> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org To: Pekka Enberg Cc: "Zhang, Yanmin" , Nick Piggin , Linux Memory Management List , Linux Kernel Mailing List , Andrew Morton , Lin Ming , Christoph Lameter List-ID: On Fri, 6 Feb 2009, Pekka Enberg wrote: > On Thu, 2009-02-05 at 19:04 +0000, Hugh Dickins wrote: > > I then tried a patch I thought obviously better than yours: just mask > > off __GFP_WAIT in that __GFP_NOWARN|__GFP_NORETRY preliminary call to > > alloc_slab_page(): so we're not trying to infer anything about high- > > order availability from the number of free order-0 pages, but actually > > going to look for it and taking it if it's free, forgetting it if not. > > > > That didn't work well at all: almost as bad as the unmodified slub.c. > > I decided that was due to __alloc_pages_internal()'s > > wakeup_kswapd(zone, order): just expressing an interest in a high- > > order page was enough to send it off trying to reclaim them, though > > not directly. Hacked in a condition to suppress that in this case: > > worked a lot better, but not nearly as well as yours. I supposed > > that was somehow(?) due to the subsequent get_page_from_freelist() > > calls with different watermarking: hacked in another __GFP flag to > > break out to nopage just like the NUMA_BUILD GFP_THISNODE case does. > > Much better, getting close, but still not as good as yours. > > Did you look at it with oprofile? No, I didn't. I didn't say so, but again it was elapsed time that I was focussing on, so I don't think oprofile would be relevant. There are some differences in system time, of course, consistent with your point; but they're generally an order of magnitude less, so didn't excite my interest. > One thing to keep in mind is that if > there are 4K allocations going on, your approach will get double the > overhead of page allocations (which can be substantial performance hit > for slab). Sure, and even the current allocate_slab() is inefficient in that respect: I've followed it because I do for now have an interest in the stats, but if stats are configured off then there's no point in dividing it into two stages; and if they are really intended to be ORDER_FALLBACK stats, then it shouldn't divide into two stages when oo_order(s->oo) == oo_order(s->min). On the other hand, I find it interesting to see how often the __GFP_NORETRY fails, even when the order is the same each time (and usually 0). Hugh -- 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