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Thu, 05 Feb 2026 21:41:51 -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 11:11:43 +0530 In-Reply-To: <20260205163217.GP7712@frogsfrogsfrogs> References: <20260116100818.7576-1-kundan.kumar@samsung.com> <20260116100818.7576-4-kundan.kumar@samsung.com> <20260129004404.GA7712@frogsfrogsfrogs> <90870969cb6f04346d6dba603838abf993a42f5b.camel@gmail.com> <20260205163217.GP7712@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: A5D96180006 X-Stat-Signature: 1kow4s5ibpqsm15o3s5xoqtm64n18y5h X-HE-Tag: 1770356513-675434 X-HE-Meta: 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 qPFLb2I3 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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 08:32 -0800, Darrick J. Wong wrote: > On Thu, Feb 05, 2026 at 12:14:35PM +0530, Nirjhar Roy (IBM) wrote: > > 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? > > I was talking about the "xfs_agp" numbers introduced in the previous > patch, which seem to contain the bottom 25 bits of the ag number. Okay, right. Thank you. > > Really I was just asking about multi-fsblock folios -- which block > within that folio do we map to an AG for tagging purposes? > > I think Kundan replied elsewhere that it's the first block. Okay. --NR > > --D > > > --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 > > > > > > > >