From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 41B3EEC7 for ; Fri, 19 Jan 2024 01:05:36 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1705626336; cv=none; b=GXDzPKyrzKjJzqhsRIoDplOQTJ4OlKSZk6mO9TJURRxbddkbp8LONoPa469OBKcnUp70j5HOgrNOgdwYbGdbUl4u4nKtYBYNx8UcenGmiO3KHrBkuZRwNa8C+/UbvvWhW5Psg7xXou+mETSOfuQaKiM+GqmGIPIv3PKxGjn60J4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1705626336; c=relaxed/simple; bh=JJIMTdptpjRLqghyqHcwxmA/ycuk6CNv+5IIAWSkqaw=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=f1Cjos2+8H0s2ZOq6lJwlC7d4uHT8ykkl2rSF0m76+iHBS4/nYWg5rrcJAC9ONwwWeW9p21mvbmpkKDs+GZx4jkFbjts3MWv0MKjcHqL2EHEUL1nK+xCJpdudTYmCqQA4XK8pXmVvF+UoH4rL/wyUQBAHZnh/RWfBoU8iRdlZ1M= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=uUuTYMCj; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="uUuTYMCj" Received: by smtp.kernel.org (Postfix) with ESMTPSA id BEA86C433C7; Fri, 19 Jan 2024 01:05:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1705626335; bh=JJIMTdptpjRLqghyqHcwxmA/ycuk6CNv+5IIAWSkqaw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=uUuTYMCjI9pzDy1xuacxfo6X2TPAD/5Z5Ef/2PS/FWlsz0yjlcz8i047TNXIsW9yw hHN4RQW7N4FxyDFnSDRwzNUabUVbDfwrEVnS73areg3028gX9deRBXEiXt8UdXDE6E TEgcpvuGE6eUE7bd1OB0zgvDJaCAmg/jfxa1ncP0oWBo5hLadrcjneo10S22qh53mb Io4dmvJcZU38ufkMqpV6lloCsQLr0y4xBCXYFpCk/lWfRy/rXPY4N4MqeRArTlpsJI 8Y9S7MJvT+SuccCEVxba7PpnuAnrWZ9+JPtcJUU4s6LRrbtj0QUnsrvKH9LQ5lS8t6 DTViiyOWZYxvg== Date: Thu, 18 Jan 2024 17:05:35 -0800 From: "Darrick J. Wong" To: Dave Chinner Cc: linux-xfs@vger.kernel.org, willy@infradead.org, linux-mm@kvack.org Subject: Re: [RFC] [PATCH 0/3] xfs: use large folios for buffers Message-ID: <20240119010535.GP674499@frogsfrogsfrogs> References: <20240118222216.4131379-1-david@fromorbit.com> Precedence: bulk X-Mailing-List: linux-xfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240118222216.4131379-1-david@fromorbit.com> On Fri, Jan 19, 2024 at 09:19:38AM +1100, Dave Chinner wrote: > The XFS buffer cache supports metadata buffers up to 64kB, and it does so by > aggregating multiple pages into a single contiguous memory region using > vmapping. This is expensive (both the setup and the runtime TLB mapping cost), > and would be unnecessary if we could allocate large contiguous memory regions > for the buffers in the first place. > > Enter multi-page folios. LOL, hch and I just wrapped up making the xfbtree buffer cache work with large folios coming from tmpfs. Though the use case there is simpler because we require blocksize==PAGE_SIZE, forbid the use of highmem, and don't need discontig buffers. Hence we sidestep vm_map_ram. :) > This patchset converts the buffer cache to use the folio API, then enhances it > to optimisitically use large folios where possible. It retains the old "vmap an > array of single page folios" functionality as a fallback when large folio > allocation fails. This means that, like page cache support for large folios, we > aren't dependent on large folio allocation succeeding all the time. > > This relegates the single page array allocation mechanism to the "slow path" > that we don't have to care so much about performance of this path anymore. This > might allow us to simplify it a bit in future. > > One of the issues with the folio conversion is that we use a couple of APIs that > take struct page ** (i.e. pointers to page pointer arrays) and there aren't > folio counterparts. These are the bulk page allocator and vm_map_ram(). In the > cases where they are used, we cast &bp->b_folios[] to (struct page **) knowing > that this array will only contain single page folios and that single page folios > and struct page are the same structure and so have the same address. This is a > bit of a hack (hence the RFC) but I'm not sure that it's worth adding folio > versions of these interfaces right now. We don't need to use the bulk page > allocator so much any more, because that's now a slow path and we could probably > just call folio_alloc() in a loop like we used to. What to do about vm_map_ram() > is a little less clear.... Yeah, that's what I suspected. > The other issue I tripped over in doing this conversion is that the > discontiguous buffer straddling code in the buf log item dirty region tracking > is broken. We don't actually exercise that code on existing configurations, and > I tripped over it when tracking down a bug in the folio conversion. I fixed it > and short-circuted the check for contiguous buffers, but that didn't fix the > failure I was seeing (which was not handling bp->b_offset and large folios > properly when building bios). Yikes. > Apart from those issues, the conversion and enhancement is relatively straight > forward. It passes fstests on both 512 and 4096 byte sector size storage (512 > byte sectors exercise the XBF_KMEM path which has non-zero bp->b_offset values) > and doesn't appear to cause any problems with large directory buffers, though I > haven't done any real testing on those yet. Large folio allocations are > definitely being exercised, though, as all the inode cluster buffers are 16kB on > a 512 byte inode V5 filesystem. > > Thoughts, comments, etc? Not yet. > Note: this patchset is on top of the NOFS removal patchset I sent a > few days ago. That can be pulled from this git branch: > > https://git.kernel.org/pub/scm/linux/kernel/git/dgc/linux-xfs.git xfs-kmem-cleanup Oooh a branch link, thank you. It's so much easier if I can pull a branch while picking through commits over gitweb. --D > >