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Thu, 05 Feb 2026 21:36:12 -0800 (PST) Message-ID: Subject: Re: [PATCH v3 3/6] xfs: add per-inode AG prediction map and dirty-AG bitmap From: "Nirjhar Roy (IBM)" To: "Darrick J. Wong" Cc: Kundan Kumar , 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 Date: Fri, 06 Feb 2026 11:06:03 +0530 In-Reply-To: <20260205163650.GQ7712@frogsfrogsfrogs> References: <20260116100818.7576-1-kundan.kumar@samsung.com> <20260116100818.7576-4-kundan.kumar@samsung.com> <87a16d4d9c1e568a37fa07a97dda5777e14e9a8b.camel@gmail.com> <20260205163650.GQ7712@frogsfrogsfrogs> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.28.5 (3.28.5-27.el8_10) Mime-Version: 1.0 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 81671A0008 X-Stat-Signature: ny471o64nmdsgegdxzmeq8iiz4qp6kys X-HE-Tag: 1770356174-285797 X-HE-Meta: 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 16mqDicY 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, 2026-02-05 at 08:36 -0800, Darrick J. Wong wrote: > On Thu, Feb 05, 2026 at 12:06:19PM +0530, Nirjhar Roy (IBM) wrote: > > On Fri, 2026-01-16 at 15:38 +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) > > Similar comment as before: > > static int > > xfs_inode_init...() > > > +{ > > > + unsigned int bits = ip->i_mount->m_sb.sb_agcount; > > > + unsigned int nlongs; > > > + > > > + xa_init_flags(&ip->i_ag_pmap, XA_FLAGS_LOCK_IRQ); > > Nit: The name of the functions suggests that it is initializing the tracking bitmap which it does - > > however, the above line does slightly different thing? Maybe move the xarray init outside the bitmap > > init function? > > Or just call it something else? xfs_inode_init_perag_wb? > > > > + ip->i_ag_dirty_bitmap = NULL; > > > + ip->i_ag_dirty_bits = bits; > > > + > > > + if (!bits) > > Umm, !bits means agcount is 0. Shouldn't we ASSERT that bits >= 2? Or am I missing something? > > Technically you can have 1 AG, but you definitely can't mount a zero AG > filesystem. Okay, but: /home/ubuntu$ mkfs.xfs -f -d agcount=1 /dev/loop0 Filesystem must have at least 2 superblocks for redundancy! Usage: mkfs.xfs Or maybe this restriction is just at the userspace tool level? > > > > + return 0; > > > + > > > + nlongs = BITS_TO_LONGS(bits); > > > + ip->i_ag_dirty_bitmap = kcalloc(nlongs, sizeof(unsigned long), > > > + GFP_NOFS); > > > + > > > + 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); > > xfs_inode_init_ag_bitmap() returns int - error handling for -ENOMEM? > > > + > > > 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); > > Nit:Maybe have a small wrapper for freeing it the prediction map? No hard preferences though. > > > + kfree(ip->i_ag_dirty_bitmap); > > > + ip->i_ag_dirty_bitmap = NULL; > > Nit: Usually while freeing the pointers I prefer: > > t = ip->i_ag_dirty_bitmap; > > ip->i_ag_dirty_bitmap = NULL; > > kfree(t); > > In this way, the pointer(i_ag_dirty_bitmap in this case) that I am freeing never points to an > > already freed address. > > > > > + 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 */ > > > + struct xarray i_ag_pmap; > > > + unsigned long *i_ag_dirty_bitmap; > > > + unsigned int i_ag_dirty_bits; > > Not sure but, I mostly see the typedefed versions of data types being used like uint32 etc. Darrick, > > hch, are the above fine? > > Yes, please don't mix types. Pick one type and stick with it. > > (and yes I wish we could struct bitmap_t(unsigned long)) > > --D > > > --NR > > > } xfs_inode_t; > > > > > > static inline bool xfs_inode_on_unlinked_list(const struct xfs_inode *ip)