From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (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 1BF353A2549 for ; Wed, 18 Mar 2026 11:44:43 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773834287; cv=none; b=kn9c7i3srUGgpPtKkYUYU5EnnxRvMCn+4VIHjEPkGjlvLajb8dDROfN+v3oD69sjHzkVYsz4Jbpiv+E+iOMhM1BlEIhm8TKH+DTdskDpY3E4FyZm9AtH1qw4BL4fvmP8s/nfZgEfaGPmzQqAjc0SCAi2raPCBXcQQw2a1UcWz4U= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773834287; c=relaxed/simple; bh=MnnB2YPUhBuztU+MB6IeMx9vtfF+8SffQRsF5EuLw8A=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=QHhDvrmiRI9/ZWutKcHx3UGqTDZpgk5Q8zFdbwAGRKW7BrAcM/Ux9wHS327E3G8nwrSgnqKesYAfRalqtdcrk7B5pHNPcj5lvf5E3Q7ulrMXdpkbFzWyMuxvjwVF86J0KQ4Tb9pNX1zgrubPxE7G5XWpA3hqV46eB8ARTBzG1Ss= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=OBNSjloT; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="OBNSjloT" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1773834282; 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=r8hOsrzuco3wh7k6MMgwBzXvoJm2wLCgxalWQx1D5/A=; b=OBNSjloTX0veG3m64TATEHgCs9eZevMOENi5mUKoFPnZPRDZnfTLu9lCtbUtQxCGrzbXIF Qc1/ou5KIpAMcV2RlUzOGKcmbGiNCcXWomyXvIC8e6Cwd0t9wtPvqSKYU4/+8EScTxf/+s ASv/QSpngtvcs3PWHn08PqbyDxi3lEw= Received: from mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-601-x7Jd4HhyOTaktJq93-CVOw-1; Wed, 18 Mar 2026 07:44:39 -0400 X-MC-Unique: x7Jd4HhyOTaktJq93-CVOw-1 X-Mimecast-MFC-AGG-ID: x7Jd4HhyOTaktJq93-CVOw_1773834278 Received: from mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.111]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 5714018005B3; Wed, 18 Mar 2026 11:44:38 +0000 (UTC) Received: from bfoster (unknown [10.22.89.178]) by mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 28A731800351; Wed, 18 Mar 2026 11:44:36 +0000 (UTC) Date: Wed, 18 Mar 2026 07:44:34 -0400 From: Brian Foster To: Christoph Hellwig Cc: Carlos Maiolino , Dave Chinner , linux-xfs@vger.kernel.org, "Darrick J. Wong" Subject: Re: [PATCH 1/4] xfs: don't keep a reference for buffers on the LRU Message-ID: References: <20260317134110.1691097-1-hch@lst.de> <20260317134110.1691097-2-hch@lst.de> 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: <20260317134110.1691097-2-hch@lst.de> X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.111 On Tue, Mar 17, 2026 at 02:40:52PM +0100, Christoph Hellwig wrote: > Currently the buffer cache adds a reference to b_hold for buffers that > are on the LRU. This seems to go all the way back and allows releasing > buffers from the LRU using xfs_buf_rele. But it makes xfs_buf_rele > really complicated in differs from how other LRUs are implemented in > Linux. > > Switch to not having a reference for buffers in the LRU, and use a > separate negative hold value to mark buffers as dead. This simplifies > xfs_buf_rele, which now just deal with the last "real" reference, > and prepares for using the lockref primitive. > > This also removes the b_lock protection for removing buffers from the > buffer hash. This is the desired outcome because the rhashtable is > fully internally synchronized, and previously the lock was mostly > held out of ordering constrains in xfs_buf_rele_cached. > > Signed-off-by: Christoph Hellwig > Reviewed-by: "Darrick J. Wong" > --- > fs/xfs/xfs_buf.c | 139 ++++++++++++++++++----------------------------- > fs/xfs/xfs_buf.h | 8 +-- > 2 files changed, 53 insertions(+), 94 deletions(-) > > diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c > index d2f3c50d80e7..3cd37f082a69 100644 > --- a/fs/xfs/xfs_buf.c > +++ b/fs/xfs/xfs_buf.c ... > @@ -1610,11 +1564,12 @@ xfs_buftarg_isolate( > struct list_head *dispose = arg; > > /* > - * we are inverting the lru lock/bp->b_lock here, so use a trylock. > - * If we fail to get the lock, just skip it. > + * We are inverting the lru lock vs bp->b_lock order here, so use a > + * trylock. If we fail to get the lock, just skip the buffer. > */ > if (!spin_trylock(&bp->b_lock)) > return LRU_SKIP; > + > /* > * Decrement the b_lru_ref count unless the value is already > * zero. If the value is already zero, we need to reclaim the > @@ -1624,8 +1579,18 @@ xfs_buftarg_isolate( > spin_unlock(&bp->b_lock); > return LRU_ROTATE; > } > + (Trailing) Whitespace damage here ^, JFYI. Otherwise LGTM. I like Dave's suggestion, but either way: Reviewed-by: Brian Foster > + /* > + * If the buffer is in use, remove it from the LRU for now as we can't > + * free it. It will be freed when the last reference drops. > + */ > + if (bp->b_hold > 0) { > + list_lru_isolate(lru, &bp->b_lru); > + spin_unlock(&bp->b_lock); > + return LRU_REMOVED; > + } > > - bp->b_state |= XFS_BSTATE_DISPOSE; > + bp->b_hold = -1; > list_lru_isolate_move(lru, item, dispose); > spin_unlock(&bp->b_lock); > return LRU_REMOVED; > @@ -1647,7 +1612,7 @@ xfs_buftarg_shrink_scan( > struct xfs_buf *bp; > bp = list_first_entry(&dispose, struct xfs_buf, b_lru); > list_del_init(&bp->b_lru); > - xfs_buf_rele(bp); > + xfs_buf_destroy(bp); > } > > return freed; > diff --git a/fs/xfs/xfs_buf.h b/fs/xfs/xfs_buf.h > index e25cd2a160f3..e7324d58bd96 100644 > --- a/fs/xfs/xfs_buf.h > +++ b/fs/xfs/xfs_buf.h > @@ -68,11 +68,6 @@ typedef unsigned int xfs_buf_flags_t; > { XBF_INCORE, "INCORE" }, \ > { XBF_TRYLOCK, "TRYLOCK" } > > -/* > - * Internal state flags. > - */ > -#define XFS_BSTATE_DISPOSE (1 << 0) /* buffer being discarded */ > - > struct xfs_buf_cache { > struct rhashtable bc_hash; > }; > @@ -159,7 +154,7 @@ struct xfs_buf { > > xfs_daddr_t b_rhash_key; /* buffer cache index */ > int b_length; /* size of buffer in BBs */ > - unsigned int b_hold; /* reference count */ > + int b_hold; /* reference count */ > atomic_t b_lru_ref; /* lru reclaim ref count */ > xfs_buf_flags_t b_flags; /* status flags */ > struct semaphore b_sema; /* semaphore for lockables */ > @@ -170,7 +165,6 @@ struct xfs_buf { > */ > struct list_head b_lru; /* lru list */ > spinlock_t b_lock; /* internal state lock */ > - unsigned int b_state; /* internal state flags */ > wait_queue_head_t b_waiters; /* unpin waiters */ > struct list_head b_list; > struct xfs_perag *b_pag; > -- > 2.47.3 > >