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Wed, 04 Feb 2026 22:36:30 -0800 (PST) Message-ID: <87a16d4d9c1e568a37fa07a97dda5777e14e9a8b.camel@gmail.com> Subject: Re: [PATCH v3 3/6] xfs: add per-inode AG prediction map and dirty-AG bitmap From: "Nirjhar Roy (IBM)" To: 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, djwong@kernel.org, dave@stgolabs.net, cem@kernel.org, wangyufei@vivo.com Cc: 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: Thu, 05 Feb 2026 12:06:19 +0530 In-Reply-To: <20260116100818.7576-4-kundan.kumar@samsung.com> References: <20260116100818.7576-1-kundan.kumar@samsung.com> <20260116100818.7576-4-kundan.kumar@samsung.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.28.5 (3.28.5-27.el8_10) Precedence: bulk X-Mailing-List: linux-xfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Transfer-Encoding: 7bit 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? > + 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? > + 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? --NR > } xfs_inode_t; > > static inline bool xfs_inode_on_unlinked_list(const struct xfs_inode *ip)