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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: <20260129004404.GA7712@frogsfrogsfrogs> References: <20260116100818.7576-1-kundan.kumar@samsung.com> <20260116100818.7576-4-kundan.kumar@samsung.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260116100818.7576-4-kundan.kumar@samsung.com> X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 7E214140002 X-Stat-Signature: yatara5hd7f76gwpkbfd136egkee6gft X-Rspam-User: X-HE-Tag: 1769647446-912801 X-HE-Meta: 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 3LJKCLJQ ZvDXu0ydwCLVXChg62z9BsDUO+dKEzUdmnmgmFgnb0o30py73FvFonm4X6dc7tEJwyWuaCsLeTYgNI7u2bc5svDs20TEGSTXJTNkhyunsgHdLwi3SvpxSqeraIBm98TsZHKqXZKCyFyDdC6qrkfAoHOa3I2lZd5Y4yH5fkBMcw3qtF2LitghfQfG6cHWC4BprpF15XHyzsXlLjP+v0zDbh+80hFp1ThZZVIg8vE9SE+H6eR9bNfE2jvsD7ERusj7gMW9aMl8V/gGW2922G6+hSLPjJiJjLe3FU7vfNdh7y8dFEHKQADp74DhH2050bgxVOXF1f8HttNWkS1+4lEXZ9JV4dbNNdv0Ttx4vjQ+jBFoIpAknKdPpe0GnJ/zgmN/ZCBLJ 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 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? 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 > >