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=-16.2 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 EFD37C433DB for ; Wed, 10 Mar 2021 23:01:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BDEAD64FC3 for ; Wed, 10 Mar 2021 23:01:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230499AbhCJXBT (ORCPT ); Wed, 10 Mar 2021 18:01:19 -0500 Received: from mail.kernel.org ([198.145.29.99]:34684 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231368AbhCJXBP (ORCPT ); Wed, 10 Mar 2021 18:01:15 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id ED77164F60; Wed, 10 Mar 2021 23:01:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1615417275; bh=wtn6duQ6Vp1jks7ke0wFBC3MJ/mmuTGEk9wI+wW/10E=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=arrvYprXYb/6aVIf7mOx3kwJACY80ZZVhihruuwDVxB/UIB0DcU023MyLtriWgZQp 1/PvShkfzo266+4CMOUL6Z7djqakp5i8AetGFK1ADDoTMULh54Xg3BDLRZocoZYw9v H75oDcznzlNJkCkPrVNb7nQpQJQVdC0K/Lc4u0eziwSdY+LmorNGQhzwjQSshIZHeV O4J0KHQsBn379AUUHE2yPaf84OA8KX/h226htnGoeVsAWezitpNLI5wWn2TkSb4tQZ g4gNQKhvmFkt/dErw3tvRDviXn69YlM6rCIva4R0a6bUQLl33ALr6qliNb73Y847Yg GJUCqAlStEhQw== Date: Wed, 10 Mar 2021 15:01:11 -0800 From: "Darrick J. Wong" To: Dave Chinner Cc: linux-xfs@vger.kernel.org Subject: Re: [PATCH 32/45] xfs: use the CIL space used counter for emptiness checks Message-ID: <20210310230111.GF3419940@magnolia> References: <20210305051143.182133-1-david@fromorbit.com> <20210305051143.182133-33-david@fromorbit.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210305051143.182133-33-david@fromorbit.com> Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org On Fri, Mar 05, 2021 at 04:11:30PM +1100, Dave Chinner wrote: > From: Dave Chinner > > In the next patches we are going to make the CIL list itself > per-cpu, and so we cannot use list_empty() to check is the list is > empty. Replace the list_empty() checks with a flag in the CIL to > indicate we have committed at least one transaction to the CIL and > hence the CIL is not empty. > > We need this flag to be an atomic so that we can clear it without > holding any locks in the commit fast path, but we also need to be > careful to avoid atomic operations in the fast path. Hence we use > the fact that test_bit() is not an atomic op to first check if the > flag is set and then run the atomic test_and_clear_bit() operation > to clear it and steal the initial unit reservation for the CIL > context checkpoint. > > When we are switching to a new context in a push, we place the > setting of the XLOG_CIL_EMPTY flag under the xc_push_lock. THis > allows all the other places that need to check whether the CIL is > empty to use test_bit() and still be serialised correctly with the > CIL context swaps that set the bit. > > Signed-off-by: Dave Chinner > --- > fs/xfs/xfs_log_cil.c | 49 +++++++++++++++++++++++-------------------- > fs/xfs/xfs_log_priv.h | 4 ++++ > 2 files changed, 30 insertions(+), 23 deletions(-) > > diff --git a/fs/xfs/xfs_log_cil.c b/fs/xfs/xfs_log_cil.c > index 4047f95a0fc4..e6e36488f0c7 100644 > --- a/fs/xfs/xfs_log_cil.c > +++ b/fs/xfs/xfs_log_cil.c > @@ -70,6 +70,7 @@ xlog_cil_ctx_switch( > struct xfs_cil *cil, > struct xfs_cil_ctx *ctx) > { > + set_bit(XLOG_CIL_EMPTY, &cil->xc_flags); > ctx->sequence = ++cil->xc_current_sequence; > ctx->cil = cil; > cil->xc_ctx = ctx; > @@ -436,13 +437,12 @@ xlog_cil_insert_items( > list_splice_init(&tp->t_busy, &ctx->busy_extents); > > /* > - * Now transfer enough transaction reservation to the context ticket > - * for the checkpoint. The context ticket is special - the unit > - * reservation has to grow as well as the current reservation as we > - * steal from tickets so we can correctly determine the space used > - * during the transaction commit. > + * We need to take the CIL checkpoint unit reservation on the first > + * commit into the CIL. Test the XLOG_CIL_EMPTY bit first so we don't > + * unnecessarily do an atomic op in the fast path here. > */ > - if (ctx->ticket->t_curr_res == 0) { > + if (test_bit(XLOG_CIL_EMPTY, &cil->xc_flags) && > + test_and_clear_bit(XLOG_CIL_EMPTY, &cil->xc_flags)) { Hm, it'll be amusing to see where this goes. Usually I tell myself in siutations like these "I think this is ok, let's see where we are in another 4-5 patches" but now I'm 7 patches out and my brain is getting close to ENOSPC so I'll tentatively say: Reviewed-by: Darrick J. Wong With the caveat that I could have more to say after the fact... --D > ctx_res = ctx->ticket->t_unit_res; > ctx->ticket->t_curr_res = ctx_res; > tp->t_ticket->t_curr_res -= ctx_res; > @@ -771,7 +771,7 @@ xlog_cil_push_work( > * move on to a new sequence number and so we have to be able to push > * this sequence again later. > */ > - if (list_empty(&cil->xc_cil)) { > + if (test_bit(XLOG_CIL_EMPTY, &cil->xc_flags)) { > cil->xc_push_seq = 0; > spin_unlock(&cil->xc_push_lock); > goto out_skip; > @@ -1019,9 +1019,10 @@ xlog_cil_push_background( > > /* > * The cil won't be empty because we are called while holding the > - * context lock so whatever we added to the CIL will still be there > + * context lock so whatever we added to the CIL will still be there. > */ > ASSERT(!list_empty(&cil->xc_cil)); > + ASSERT(!test_bit(XLOG_CIL_EMPTY, &cil->xc_flags)); > > /* > * Don't do a background push if we haven't used up all the > @@ -1108,7 +1109,8 @@ xlog_cil_push_now( > * there's no work we need to do. > */ > spin_lock(&cil->xc_push_lock); > - if (list_empty(&cil->xc_cil) || push_seq <= cil->xc_push_seq) { > + if (test_bit(XLOG_CIL_EMPTY, &cil->xc_flags) || > + push_seq <= cil->xc_push_seq) { > spin_unlock(&cil->xc_push_lock); > return; > } > @@ -1128,7 +1130,7 @@ xlog_cil_empty( > bool empty = false; > > spin_lock(&cil->xc_push_lock); > - if (list_empty(&cil->xc_cil)) > + if (test_bit(XLOG_CIL_EMPTY, &cil->xc_flags)) > empty = true; > spin_unlock(&cil->xc_push_lock); > return empty; > @@ -1289,7 +1291,7 @@ xlog_cil_force_seq( > * we would have found the context on the committing list. > */ > if (sequence == cil->xc_current_sequence && > - !list_empty(&cil->xc_cil)) { > + !test_bit(XLOG_CIL_EMPTY, &cil->xc_flags)) { > spin_unlock(&cil->xc_push_lock); > goto restart; > } > @@ -1320,21 +1322,19 @@ xlog_cil_force_seq( > */ > bool > xfs_log_item_in_current_chkpt( > - struct xfs_log_item *lip) > + struct xfs_log_item *lip) > { > - struct xfs_cil_ctx *ctx; > + struct xfs_cil *cil = lip->li_mountp->m_log->l_cilp; > > - if (list_empty(&lip->li_cil)) > + if (test_bit(XLOG_CIL_EMPTY, &cil->xc_flags)) > return false; > > - ctx = lip->li_mountp->m_log->l_cilp->xc_ctx; > - > /* > * li_seq is written on the first commit of a log item to record the > * first checkpoint it is written to. Hence if it is different to the > * current sequence, we're in a new checkpoint. > */ > - if (XFS_LSN_CMP(lip->li_seq, ctx->sequence) != 0) > + if (XFS_LSN_CMP(lip->li_seq, cil->xc_ctx->sequence) != 0) > return false; > return true; > } > @@ -1373,13 +1373,16 @@ void > xlog_cil_destroy( > struct xlog *log) > { > - if (log->l_cilp->xc_ctx) { > - if (log->l_cilp->xc_ctx->ticket) > - xfs_log_ticket_put(log->l_cilp->xc_ctx->ticket); > - kmem_free(log->l_cilp->xc_ctx); > + struct xfs_cil *cil = log->l_cilp; > + > + if (cil->xc_ctx) { > + if (cil->xc_ctx->ticket) > + xfs_log_ticket_put(cil->xc_ctx->ticket); > + kmem_free(cil->xc_ctx); > } > > - ASSERT(list_empty(&log->l_cilp->xc_cil)); > - kmem_free(log->l_cilp); > + ASSERT(list_empty(&cil->xc_cil)); > + ASSERT(test_bit(XLOG_CIL_EMPTY, &cil->xc_flags)); > + kmem_free(cil); > } > > diff --git a/fs/xfs/xfs_log_priv.h b/fs/xfs/xfs_log_priv.h > index 003c11653955..b0dc3bc9de59 100644 > --- a/fs/xfs/xfs_log_priv.h > +++ b/fs/xfs/xfs_log_priv.h > @@ -248,6 +248,7 @@ struct xfs_cil_ctx { > */ > struct xfs_cil { > struct xlog *xc_log; > + unsigned long xc_flags; > struct list_head xc_cil; > spinlock_t xc_cil_lock; > > @@ -263,6 +264,9 @@ struct xfs_cil { > wait_queue_head_t xc_push_wait; /* background push throttle */ > } ____cacheline_aligned_in_smp; > > +/* xc_flags bit values */ > +#define XLOG_CIL_EMPTY 1 > + > /* > * The amount of log space we allow the CIL to aggregate is difficult to size. > * Whatever we choose, we have to make sure we can get a reservation for the > -- > 2.28.0 >