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 X-Spam-Level: X-Spam-Status: No, score=-16.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A29B0C433E0 for ; Wed, 24 Feb 2021 21:30:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 64FE164F0D for ; Wed, 24 Feb 2021 21:30:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232533AbhBXVaN (ORCPT ); Wed, 24 Feb 2021 16:30:13 -0500 Received: from mail.kernel.org ([198.145.29.99]:49230 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232245AbhBXVaN (ORCPT ); Wed, 24 Feb 2021 16:30:13 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 3475064F0D; Wed, 24 Feb 2021 21:29:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1614202170; bh=BEZMZMs1G2XDtOOI0w6OLJpqtIsQN2MjswXN7nX7I+o=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=po2yaIWtltvOaQMq7VCwQ1ZoM4ZYcUoWugM5wZiE1WfDHRhMNkToxJpBawZAj6V0l g7a8UWjbUv3Jb9M7QZl2egWXAQm5sMXGklyJVtWWp9VaDMXKC8nT9Gq/VXSUgpoN3J XCzyXTcs+UkdaBkipuz8R4plu3DT0ey6zW3bF+A4CWU0QCqhboT3YWjr1VPvv6XxBi 5SfRUMsROV0Mbg/9Crs28hoaGpx9Y8pAMRMGsWmkiIK1+FbtBD/cXFUvEgUyLeFvKd bFDb4NIOiAqRhrnzSkH7GQBTFSV4pyUsp+Z9yXYHY5LEb1BP5EoyRP09BqXTCIxPxB rNhkBOj3DjI/A== Date: Wed, 24 Feb 2021 13:29:29 -0800 From: "Darrick J. Wong" To: Dave Chinner Cc: linux-xfs@vger.kernel.org Subject: Re: [PATCH 1/3] xfs: reduce buffer log item shadow allocations Message-ID: <20210224212929.GY7272@magnolia> References: <20210223044636.3280862-1-david@fromorbit.com> <20210223044636.3280862-2-david@fromorbit.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210223044636.3280862-2-david@fromorbit.com> Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org On Tue, Feb 23, 2021 at 03:46:34PM +1100, Dave Chinner wrote: > From: Dave Chinner > > When we modify btrees repeatedly, we regularly increase the size of > the logged region by a single chunk at a time (per transaction > commit). This results in the CIL formatting code having to > reallocate the log vector buffer every time the buffer dirty region > grows. Hence over a typical 4kB btree buffer, we might grow the log > vector 4096/128 = 32x over a short period where we repeatedly add > or remove records to/from the buffer over a series of running > transaction. This means we are doing 32 memory allocations and frees > over this time during a performance critical path in the journal. > > The amount of space tracked in the CIL for the object is calculated > during the ->iop_format() call for the buffer log item, but the > buffer memory allocated for it is calculated by the ->iop_size() > call. The size callout determines the size of the buffer, the format > call determines the space used in the buffer. > > Hence we can oversize the buffer space required in the size > calculation without impacting the amount of space used and accounted > to the CIL for the changes being logged. This allows us to reduce > the number of allocations by rounding up the buffer size to allow > for future growth. This can safe a substantial amount of CPU time in > this path: > > - 46.52% 2.02% [kernel] [k] xfs_log_commit_cil > - 44.49% xfs_log_commit_cil > - 30.78% _raw_spin_lock > - 30.75% do_raw_spin_lock > 30.27% __pv_queued_spin_lock_slowpath > > (oh, ouch!) > .... > - 1.05% kmem_alloc_large > - 1.02% kmem_alloc > 0.94% __kmalloc > > This overhead here us what this patch is aimed at. After: > > - 0.76% kmem_alloc_large > - 0.75% kmem_alloc > 0.70% __kmalloc > > Signed-off-by: Dave Chinner > Reviewed-by: Chandan Babu R Any particular reason for 512? It looks like you simply picked an arbitrary power of 2, but was there a particular target in mind? i.e. we never need to realloc for the usual 4k filesystem? Reviewed-by: Darrick J. Wong --D > --- > fs/xfs/xfs_buf_item.c | 13 +++++++++++-- > 1 file changed, 11 insertions(+), 2 deletions(-) > > diff --git a/fs/xfs/xfs_buf_item.c b/fs/xfs/xfs_buf_item.c > index 17960b1ce5ef..0628a65d9c55 100644 > --- a/fs/xfs/xfs_buf_item.c > +++ b/fs/xfs/xfs_buf_item.c > @@ -142,6 +142,7 @@ xfs_buf_item_size( > { > struct xfs_buf_log_item *bip = BUF_ITEM(lip); > int i; > + int bytes; > > ASSERT(atomic_read(&bip->bli_refcount) > 0); > if (bip->bli_flags & XFS_BLI_STALE) { > @@ -173,7 +174,7 @@ xfs_buf_item_size( > } > > /* > - * the vector count is based on the number of buffer vectors we have > + * The vector count is based on the number of buffer vectors we have > * dirty bits in. This will only be greater than one when we have a > * compound buffer with more than one segment dirty. Hence for compound > * buffers we need to track which segment the dirty bits correspond to, > @@ -181,10 +182,18 @@ xfs_buf_item_size( > * count for the extra buf log format structure that will need to be > * written. > */ > + bytes = 0; > for (i = 0; i < bip->bli_format_count; i++) { > xfs_buf_item_size_segment(bip, &bip->bli_formats[i], > - nvecs, nbytes); > + nvecs, &bytes); > } > + > + /* > + * Round up the buffer size required to minimise the number of memory > + * allocations that need to be done as this item grows when relogged by > + * repeated modifications. > + */ > + *nbytes = round_up(bytes, 512); > trace_xfs_buf_item_size(bip); > } > > -- > 2.28.0 >