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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1B5B6C433EF for ; Wed, 13 Oct 2021 21:14:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EA12F61154 for ; Wed, 13 Oct 2021 21:14:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229795AbhJMVQj (ORCPT ); Wed, 13 Oct 2021 17:16:39 -0400 Received: from mail107.syd.optusnet.com.au ([211.29.132.53]:53956 "EHLO mail107.syd.optusnet.com.au" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229771AbhJMVQi (ORCPT ); Wed, 13 Oct 2021 17:16:38 -0400 Received: from dread.disaster.area (pa49-195-238-16.pa.nsw.optusnet.com.au [49.195.238.16]) by mail107.syd.optusnet.com.au (Postfix) with ESMTPS id 2830910698E3; Thu, 14 Oct 2021 08:14:33 +1100 (AEDT) Received: from dave by dread.disaster.area with local (Exim 4.92.3) (envelope-from ) id 1mala3-005uBm-OA; Thu, 14 Oct 2021 08:14:31 +1100 Date: Thu, 14 Oct 2021 08:14:31 +1100 From: Dave Chinner To: "Darrick J. Wong" Cc: Chandan Babu R , Christoph Hellwig , linux-xfs@vger.kernel.org Subject: Re: [PATCH 05/15] xfs: support dynamic btree cursor heights Message-ID: <20211013211431.GK2361455@dread.disaster.area> References: <163408155346.4151249.8364703447365270670.stgit@magnolia> <163408158126.4151249.1899753599807152513.stgit@magnolia> <20211013053122.GX2361455@dread.disaster.area> <20211013165218.GV24307@magnolia> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20211013165218.GV24307@magnolia> X-Optus-CM-Score: 0 X-Optus-CM-Analysis: v=2.4 cv=e9dl9Yl/ c=1 sm=1 tr=0 ts=61674c39 a=DzKKRZjfViQTE5W6EVc0VA==:117 a=DzKKRZjfViQTE5W6EVc0VA==:17 a=kj9zAlcOel0A:10 a=8gfv0ekSlNoA:10 a=VwQbUJbxAAAA:8 a=yPCof4ZbAAAA:8 a=7-415B0cAAAA:8 a=t6GgW1ErH5tUXTEaQsgA:9 a=CjuIK1q_8ugA:10 a=AjGcO6oz07-iQ99wixmX:22 a=biEYGPWJfzWAr4FL6Ov7:22 Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org On Wed, Oct 13, 2021 at 09:52:18AM -0700, Darrick J. Wong wrote: > On Wed, Oct 13, 2021 at 04:31:22PM +1100, Dave Chinner wrote: > > On Tue, Oct 12, 2021 at 04:33:01PM -0700, Darrick J. Wong wrote: > > > From: Darrick J. Wong > > > > > > Split out the btree level information into a separate struct and put it > > > at the end of the cursor structure as a VLA. The realtime rmap btree > > > (which is rooted in an inode) will require the ability to support many > > > more levels than a per-AG btree cursor, which means that we're going to > > > create two btree cursor caches to conserve memory for the more common > > > case. > > > > > > Signed-off-by: Darrick J. Wong > > > Reviewed-by: Chandan Babu R > > > Reviewed-by: Christoph Hellwig > > > --- > > > fs/xfs/libxfs/xfs_alloc.c | 6 +- > > > fs/xfs/libxfs/xfs_bmap.c | 10 +-- > > > fs/xfs/libxfs/xfs_btree.c | 168 +++++++++++++++++++++++---------------------- > > > fs/xfs/libxfs/xfs_btree.h | 28 ++++++-- > > > fs/xfs/scrub/bitmap.c | 22 +++--- > > > fs/xfs/scrub/bmap.c | 2 - > > > fs/xfs/scrub/btree.c | 47 +++++++------ > > > fs/xfs/scrub/trace.c | 7 +- > > > fs/xfs/scrub/trace.h | 10 +-- > > > fs/xfs/xfs_super.c | 2 - > > > fs/xfs/xfs_trace.h | 2 - > > > 11 files changed, 164 insertions(+), 140 deletions(-) > > > > Hmmm - subject of the patch doesn't really match the changes being > > made - there's nothing here that makes the btree cursor heights > > dynamic. It's just a structure layout change... > > "xfs: prepare xfs_btree_cur for dynamic cursor heights" ? *nod* > > > @@ -922,11 +922,11 @@ xfs_btree_readahead( > > > (lev == cur->bc_nlevels - 1)) > > > return 0; > > > > > > - if ((cur->bc_ra[lev] | lr) == cur->bc_ra[lev]) > > > + if ((cur->bc_levels[lev].ra | lr) == cur->bc_levels[lev].ra) > > > return 0; > > > > That's whacky logic. Surely that's just: > > > > if (cur->bc_levels[lev].ra & lr) > > return 0; > > This is an early-exit test, which means the careful check is necessary. > > If (some day) someone calls this function with (LEFTRA|RIGHTRA) to > readahead both siblings on a btree level where one sibling has been ra'd > but not the other, we must avoid taking the branch. Which I didn't see any callers do, so I ignored that possibility. Regardless, it's the use of "|" to do an additive mask match that makes it look wierd. i.e. the normal way of writing a multi-biti mask match is to apply the mask and check that the returned value matches the mask, like so: if ((cur->bc_levels[lev].ra & lr) == lr) return 0; Really, though, this was just another "ObHuh" comment, and you don't need to "fix" it now... > > > @@ -242,8 +250,17 @@ struct xfs_btree_cur > > > struct xfs_btree_cur_ag bc_ag; > > > struct xfs_btree_cur_ino bc_ino; > > > }; > > > + > > > + /* Must be at the end of the struct! */ > > > + struct xfs_btree_level bc_levels[]; > > > }; > > > > > > +static inline size_t > > > +xfs_btree_cur_sizeof(unsigned int nlevels) > > > +{ > > > + return struct_size((struct xfs_btree_cur *)NULL, bc_levels, nlevels); > > > +} > > > > Ooooh, yeah, we really need comments explaining how many btree > > levels these VLAs are tracking, because this one doesn't have a "- > > 1" in it like the previous one I commented on.... > > /* > * Compute the size of a btree cursor that can handle a btree of a given > * height. The bc_levels array handles node and leaf blocks, so its > * size is exactly nlevels. > */ Nice. Thanks! > > > diff --git a/fs/xfs/scrub/trace.c b/fs/xfs/scrub/trace.c > > > index c0ef53fe6611..816dfc8e5a80 100644 > > > --- a/fs/xfs/scrub/trace.c > > > +++ b/fs/xfs/scrub/trace.c > > > @@ -21,10 +21,11 @@ xchk_btree_cur_fsbno( > > > struct xfs_btree_cur *cur, > > > int level) > > > { > > > - if (level < cur->bc_nlevels && cur->bc_bufs[level]) > > > + if (level < cur->bc_nlevels && cur->bc_levels[level].bp) > > > return XFS_DADDR_TO_FSB(cur->bc_mp, > > > - xfs_buf_daddr(cur->bc_bufs[level])); > > > - if (level == cur->bc_nlevels - 1 && cur->bc_flags & XFS_BTREE_LONG_PTRS) > > > + xfs_buf_daddr(cur->bc_levels[level].bp)); > > > + else if (level == cur->bc_nlevels - 1 && > > > + cur->bc_flags & XFS_BTREE_LONG_PTRS) > > > > No need for an else there as the first if () clause returns. > > Also, needs more () around that "a & b" second line. > > TBH I think we check the wrong flag, and that last bit should be: > > if (level == cur->bc_nlevels - 1 && > (cur->bc_flags & XFS_BTREE_ROOT_IN_INODE)) > return XFS_INO_TO_FSB(cur->bc_mp, cur->bc_ino.ip->i_ino); > > return NULLFSBLOCK; Yup, true, long ptrs and inodes are currently interchangable so it works, but that's a landmine waiting to pounce.... > But for now I'll stick to the straight replacement and tack on another > patch to fix that. *nod*. Cheers, Dave. -- Dave Chinner david@fromorbit.com