From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 CB56F423143; Thu, 5 Feb 2026 16:42:39 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770309759; cv=none; b=CZqKfEQOL6XW1MY8+xprRps5r76GWZ7KgxZyqRjV+sya5KG66KkiOnGf50d5JvNynedXeSOjxUuG3eEeIDKnabrCmsbWMm5p8JDQVYtgxCpETy8btc5cFd7eMG2Ij+z3PPh0aP1lakQWC1z1BpSNAdT6ZYtH3VhG1y4xgZgih5c= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770309759; c=relaxed/simple; bh=qtCIuwxbUz6nAxAm44y57E2QMBh06l1dKLAKWSKgEDA=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=dzNeVyJKLGuLkoXwHu/hDBd5ure52/h/Ka6qZCql5mu9/ZuMAEZ71RGibrU6BGMACZh0gFd6lagnWU0lstoswntchXO5xMptDWp2BPFaRdyxq9hVjjCBIAZpJedCObpiCvydO5Dfgk6EsRiXtVvWVFCWlFR48CpgQ/WCK/6L5G4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=IIHoEhLf; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="IIHoEhLf" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4A177C4CEF7; Thu, 5 Feb 2026 16:42:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1770309759; bh=qtCIuwxbUz6nAxAm44y57E2QMBh06l1dKLAKWSKgEDA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=IIHoEhLfk5gLa6aiZb8rIG5WH5MvQz2EcqscXHWOJSfjO9XtyLKuihjRP4fkRIDuv xQ5tqTAHKA7tlox5BoOiDOKTYW0zOvTxvWqnMz9Qk9kb+RBflXQnKCh3b9uPyhv6m6 NMXKGnyZJ9PlM1/e+12kS4IgXvVjWG9qnpSs55GwGz+obvdjAbjxLOJfoY9GE9A22j IvLLS7PM5l7wfgzp/+Gqj8IIhKvGcMldeYPIXTFSfzSsNup6mjA3qymBryVRboUu3Z iWcYvj3APifqtCh8ulKn0JM6Vxzm6tK1HNZp7+leExEEZYA9USJEbYOH4DYsEbIrYe EVCVymgbXiqJQ== Date: Thu, 5 Feb 2026 08:42:38 -0800 From: "Darrick J. Wong" To: Kundan Kumar Cc: viro@zeniv.linux.org.uk, brauner@kernel.org, jack@suse.cz, willy@infradead.org, mcgrof@kernel.org, clm@meta.com, david@fromorbit.com, amir73il@gmail.com, axboe@kernel.dk, hch@lst.de, ritesh.list@gmail.com, dave@stgolabs.net, cem@kernel.org, wangyufei@vivo.com, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-xfs@vger.kernel.org, gost.dev@samsung.com, anuj20.g@samsung.com, vishak.g@samsung.com, joshi.k@samsung.com Subject: Re: [PATCH v3 3/6] xfs: add per-inode AG prediction map and dirty-AG bitmap Message-ID: <20260205164238.GS7712@frogsfrogsfrogs> References: <20260116100818.7576-1-kundan.kumar@samsung.com> <20260116100818.7576-4-kundan.kumar@samsung.com> <20260129004404.GA7712@frogsfrogsfrogs> <2c485586-83c9-4697-91fc-7b0cee697704@samsung.com> Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <2c485586-83c9-4697-91fc-7b0cee697704@samsung.com> On Tue, Feb 03, 2026 at 12:50:53PM +0530, Kundan Kumar wrote: > On 1/29/2026 6:14 AM, Darrick J. Wong wrote: > > On Fri, Jan 16, 2026 at 03:38:15PM +0530, Kundan Kumar wrote: > >> Add per-inode structures to track predicted AGs of dirty folios using > >> an xarray and bitmap. This enables efficient identification of AGs > >> involved in writeback. > >> > >> Signed-off-by: Kundan Kumar > >> Signed-off-by: Anuj Gupta > >> --- > >> fs/xfs/xfs_icache.c | 27 +++++++++++++++++++++++++++ > >> fs/xfs/xfs_inode.h | 5 +++++ > >> 2 files changed, 32 insertions(+) > >> > >> diff --git a/fs/xfs/xfs_icache.c b/fs/xfs/xfs_icache.c > >> index e44040206851..f97aa6d66271 100644 > >> --- a/fs/xfs/xfs_icache.c > >> +++ b/fs/xfs/xfs_icache.c > >> @@ -80,6 +80,25 @@ static inline xa_mark_t ici_tag_to_mark(unsigned int tag) > >> return XFS_PERAG_BLOCKGC_MARK; > >> } > >> > >> +static int xfs_inode_init_ag_bitmap(struct xfs_inode *ip) > >> +{ > >> + unsigned int bits = ip->i_mount->m_sb.sb_agcount; > >> + unsigned int nlongs; > >> + > >> + xa_init_flags(&ip->i_ag_pmap, XA_FLAGS_LOCK_IRQ); > > > > This increases the size of struct xfs_inode by 40 bytes... > > > > I’ll make this lazy and sparse: move AG writeback state behind a pointer > allocated on first use, and replace the bitmap with a sparse dirty-AG > set(xarray keyed by agno) so memory scales with AGs actually touched by > the inode. > > >> + ip->i_ag_dirty_bitmap = NULL; > >> + ip->i_ag_dirty_bits = bits; > >> + > >> + if (!bits) > >> + return 0; > >> + > >> + nlongs = BITS_TO_LONGS(bits); > >> + ip->i_ag_dirty_bitmap = kcalloc(nlongs, sizeof(unsigned long), > >> + GFP_NOFS); > > > > ...and there could be hundreds or thousands of AGs for each filesystem. > > That's a lot of kernel memory to handle this prediction stuff, and I"m > > not even sure what ag_dirty_bitmap does yet. > > > > The bit for an AG is set in ag_dirty_bitmap at write time. During > writeback, we check which AG bits are set, wake only those AG-specific > workers, and each worker scans the page cache, filters folios tagged for > its AG, and submits the I/O. > > >> + > >> + return ip->i_ag_dirty_bitmap ? 0 : -ENOMEM; > >> +} > >> + > >> /* > >> * Allocate and initialise an xfs_inode. > >> */ > >> @@ -131,6 +150,8 @@ xfs_inode_alloc( > >> ip->i_next_unlinked = NULLAGINO; > >> ip->i_prev_unlinked = 0; > >> > >> + xfs_inode_init_ag_bitmap(ip); > > > > Unchecked return value??? > > Will correct in next version > > > > >> + > >> return ip; > >> } > >> > >> @@ -194,6 +215,12 @@ xfs_inode_free( > >> ip->i_ino = 0; > >> spin_unlock(&ip->i_flags_lock); > >> > >> + /* free xarray contents (values are immediate packed ints) */ > >> + xa_destroy(&ip->i_ag_pmap); > >> + kfree(ip->i_ag_dirty_bitmap); > >> + ip->i_ag_dirty_bitmap = NULL; > >> + ip->i_ag_dirty_bits = 0; > >> + > >> __xfs_inode_free(ip); > >> } > >> > >> diff --git a/fs/xfs/xfs_inode.h b/fs/xfs/xfs_inode.h > >> index bd6d33557194..dee449168605 100644 > >> --- a/fs/xfs/xfs_inode.h > >> +++ b/fs/xfs/xfs_inode.h > >> @@ -99,6 +99,11 @@ typedef struct xfs_inode { > >> spinlock_t i_ioend_lock; > >> struct work_struct i_ioend_work; > >> struct list_head i_ioend_list; > >> + > >> + /* AG prediction map: pgoff_t -> packed u32 */ > > > > What about blocksize < pagesize filesystems? Which packed agno do you > > associate with the pgoff_t? > > > > Also, do you have an xarray entry for each pgoff_t in a large folio? > > > > --D > > > > pgoff_t here is the pagecache index (folio->index), i.e. file offset in > PAGE_SIZE units, not a filesystem block index. So blocksize < PAGE_SIZE > doesn’t change the association, the packed agno is attached to the folio > at that pagecache index. Ok, so the tag is entirely determined by the AG of the first fsblock within the folio. > We store one xarray entry per folio index (the start of the folio). We > do not create entries for each base-page inside a large folio. If a > large folio could span multiple extents/AGs, we’ll treat the hint as > advisory and tag it invalid (fallback to normal writeback routing) > rather than trying to encode per-subpage AGs. Oh, ok, so if you have the mapping and the folio at the same time you can determine that the entire large folio maps to a single extent, and tag the whole large folio as belonging to a single AG. That clears things up, thank you. It's only in the case of extreme fragmentation that a large folio gets flung at the old writeback paths, which is probably good enough anyway. --D > >> + struct xarray i_ag_pmap; > >> + unsigned long *i_ag_dirty_bitmap; > >> + unsigned int i_ag_dirty_bits; > >> } xfs_inode_t; > >> > >> static inline bool xfs_inode_on_unlinked_list(const struct xfs_inode *ip) > >> -- > >> 2.25.1 > >> > >> > > > >