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Wed, 04 Feb 2026 22:44:44 -0800 (PST) Message-ID: <90870969cb6f04346d6dba603838abf993a42f5b.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: "Darrick J. Wong" , 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 Date: Thu, 05 Feb 2026 12:14:35 +0530 In-Reply-To: <20260129004404.GA7712@frogsfrogsfrogs> References: <20260116100818.7576-1-kundan.kumar@samsung.com> <20260116100818.7576-4-kundan.kumar@samsung.com> <20260129004404.GA7712@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-Rspamd-Server: rspam11 X-Stat-Signature: gr859rncaeixkgiw9yd8f6kwb3xwewd4 X-Rspam-User: X-Rspamd-Queue-Id: 58087C0008 X-HE-Tag: 1770273886-662117 X-HE-Meta: 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 8+qijbm5 Sg23m/CT042U9xrOcLhq2iqY6WFm5n7US6mpUoSPJ6CRulEPXCeO4pCFg2w71kWThsCff0zF933uyXX0PAyDQmN2EGxYfS83qhE/d09VGJ+Prnq6QJxyjzlwWQQtUmFZyTBCDmsOE90y5gsPn6mRSgl5h/w== 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 Wed, 2026-01-28 at 16:44 -0800, 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... > > > + 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. > > > + > > + 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??? > > > + > > 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? Sorry but I am bit unfamiliar with the term packed agno? Can you please briefly explain does packed agno mean? --NR > > Also, do you have an xarray entry for each pgoff_t in a large folio? > > --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 > > > >