From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id C98B9C27C4F for ; Fri, 21 Jun 2024 20:04:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=9COVBQENN0t3oGjClhlT9+/MO8u8oPrewnmAyx93pxI=; b=xnCn1mpIGdP3DvvcFWTfidWFWY 5quMMo9dNhl5Kpb0v2SUCaX5NDChhNNxXlppn645T2mgP7u6teNOOOdff2DHMR45pSxzC/HmmuwqB FLfrcHJ7zNnKWFWKgG4LbpWtmg9JLj9Eh8jHOYNJc69UNVz1bm7v1nEWJ8fGFn1MvFSpvexC1yq81 F0UbbghT9sd26M9W3z+GnIYvMpGShgGekiNHXoKPgwFJ3xQkr89AMkjPMREI6FsL8pxVLD4fFPs2j ldT84/g/sMHfJHapx8bTZ7BvqlIeP0rfzSfc0odGC1NEHQUMbSYx8mDwoYRCwS2I6yNhFT/nVqi1S Sd9M7uuQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.97.1 #2 (Red Hat Linux)) id 1sKkV5-0000000ARJv-1NSy; Fri, 21 Jun 2024 20:04:47 +0000 Received: from casper.infradead.org ([2001:8b0:10b:1236::1]) by bombadil.infradead.org with esmtps (Exim 4.97.1 #2 (Red Hat Linux)) id 1sKkV3-0000000ARJc-08lu for linux-arm-kernel@bombadil.infradead.org; Fri, 21 Jun 2024 20:04:45 +0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=9COVBQENN0t3oGjClhlT9+/MO8u8oPrewnmAyx93pxI=; b=EXbXWiebsLfQVAfNCjLRWINX3O JXRxNKIp4lmfbWDk/OSFsTBof/FtYtHfQa7zSviQpB87qV3QjeCIA9sE7OinSQqpt++adXU0UIyFZ Rixiz2nA1xrTetQj/BJ8KCb8CKZUBs+FH6Bjn38geW4tJTKTzs7t2vT8MMy4QwjPlJ73Z0Ve1oNST WYDHId1KOfYZliP5GpvUL5ZztIoiYneacSfmwm0H16uqT8KxG5eKtOWkZZDuyInxAtnfiWbbmHSjP CdhuAmf1glg+j96InsxMHcJT+4Gp7kZXJzblQcyq2le1M603BlRdKC7u9Cu6O4INc5x3zrfQIDXpk 7ALMwvwA==; Received: from willy by casper.infradead.org with local (Exim 4.97.1 #2 (Red Hat Linux)) id 1sKkV0-00000007YT4-1sDe; Fri, 21 Jun 2024 20:04:42 +0000 Date: Fri, 21 Jun 2024 21:04:42 +0100 From: Matthew Wilcox To: Linus Torvalds Cc: Christian Brauner , Al Viro , linux-fsdevel , the arch/x86 maintainers , Linux ARM , Linux Kernel Mailing List , kernel test robot Subject: Re: FYI: path walking optimizations pending for 6.11 Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Wed, Jun 19, 2024 at 03:08:47PM -0700, Linus Torvalds wrote: > On Wed, 19 Jun 2024 at 13:45, Matthew Wilcox wrote: > > > > Funnily, I'm working on rosebush v2 today. It's in no shape to send out > > (it's failing ~all of its selftests) but *should* greatly improve the > > cache friendliness of the hash table. And it's being written with the > > dcache as its first customer. > > I'm interested to see if you can come up with something decent, but > I'm not hugely optimistic. Well, I've now come up with something _working_. There are still things to be fixed, but it might be interesting for a performance comparison. So I've pushed it out to http://git.infradead.org/?p=users/willy/pagecache.git;a=shortlog;h=refs/heads/rosebush where I hope 01.org will pick up on it and run some performance tests. > From what I saw, you planned on comparing with rhashtable hash chains of 10. That was the comparison I made (and it turns out I misunderstood rhashtable entirely; the length is where it does an emergency resize, and usually its size is such that the average hash length is <1) What I was reacting to in your email was this: : And on my arm64 machine, it turns out that the best optimization for the : load I tested would be to make that hash table smaller to actually be a : bit denser in the cache, But that's such a load-dependent optimization : that I'm not doing this. And that's exactly what rosebush does; it starts out incredibly small (512 bytes) and then resizes as the buckets overflow. So if you suspect that a denser hashtable would give you better performance, then maybe it'll help. Or maybe not; it's not like I've done thorough testing.