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,HEADER_FROM_DIFFERENT_DOMAINS, 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 138F1C43381 for ; Mon, 15 Mar 2021 14:53:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D473564F9B for ; Mon, 15 Mar 2021 14:53:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233913AbhCOOx0 (ORCPT ); Mon, 15 Mar 2021 10:53:26 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:60006 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240821AbhCOOwm (ORCPT ); Mon, 15 Mar 2021 10:52:42 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1615819960; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=9QOgJOK6EUJZDk3p6W1Xw7RvNiLdjc/ecx8fQ+HTksE=; b=fyyxum5uzNpF93QwrtHSFUo4sZDZyV2E5EXekgCC1c+kql7oyf2jjffq6VPDIRoarnDtk1 5/oUErU1UPqRi7FzVP8b2IdqbV1oWM63UeTyt3etGKFcZG1xjiYeCQipse19uXNFfNfK63 JEpRAYk6C4pbGz1T/nnvCqQZtEDOlX4= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-457-jCug1kDiMtKD3S-5koHxAQ-1; Mon, 15 Mar 2021 10:52:37 -0400 X-MC-Unique: jCug1kDiMtKD3S-5koHxAQ-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 918CA81747C; Mon, 15 Mar 2021 14:52:36 +0000 (UTC) Received: from bfoster (ovpn-112-124.rdu2.redhat.com [10.10.112.124]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 3BFC56B8F9; Mon, 15 Mar 2021 14:52:36 +0000 (UTC) Date: Mon, 15 Mar 2021 10:52:34 -0400 From: Brian Foster To: Dave Chinner Cc: linux-xfs@vger.kernel.org Subject: Re: [PATCH 10/45] xfs: reduce buffer log item shadow allocations Message-ID: References: <20210305051143.182133-1-david@fromorbit.com> <20210305051143.182133-11-david@fromorbit.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210305051143.182133-11-david@fromorbit.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org On Fri, Mar 05, 2021 at 04:11:08PM +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 > > The size of 512 bytes is based on the bitmap chunk size being 128 > bytes and that random directory entry updates almost never require > more than 3-4 128 byte regions to be logged in the directory block. > > The other observation is for per-ag btrees. When we are inserting > into a new btree block, we'll pack it from the front. Hence the > first few records land in the first 128 bytes so we log only 128 > bytes, the next 8-16 records land in the second region so now we log > 256 bytes. And so on. If we are doing random updates, it will only > allocate every 4 random 128 byte regions that are dirtied instead of > every single one. > > Any larger than 512 bytes and I noticed an increase in memory > footprint in my scalability workloads. Any less than this and I > didn't really see any significant benefit to CPU usage. > > Signed-off-by: Dave Chinner > Reviewed-by: Chandan Babu R > Reviewed-by: Darrick J. Wong > --- It looks like I have posted feedback (mostly reviewed-by tags, fwiw) on previous posts of this patch and the next three that appears to have been either ignored or lost. Brian > 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 >