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Wong" To: "Nirjhar Roy (IBM)" 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 Subject: Re: [PATCH v3 3/6] xfs: add per-inode AG prediction map and dirty-AG bitmap Message-ID: <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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <90870969cb6f04346d6dba603838abf993a42f5b.camel@gmail.com> X-Stat-Signature: 3c86tccddfsj54eabq9eaezyshekcon5 X-Rspamd-Queue-Id: 6D439180011 X-Rspam-User: X-Rspamd-Server: rspam04 X-HE-Tag: 1770309139-566461 X-HE-Meta: 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 0jnPdwOz ZjQ9PbT+ERPA8Vv/lCOkDiVnISK2rjakTq1MauDHZyKJM8MpY1NzvUAiSx4cI4GXuzWIc2q0hT0f1w4f1ngzq8LI1hU6pet5VKjIGx+DPS4fvt9HDwsF9U3UW2ElAZsilKs+jNxaAnsGJysHS8tAzJDYMnwJS1XyVc2UVt3f8aA27wfTkATCbV1KgLO3BME8fdJkITeyaPjaAbIK9dkGOojKcEgY2clNYL3VuQq/WZanLfzZni/ILukT37rGzTP3t6uKp8CGqEcrTiNgJXKboSfnsmNEoOPJIU/VqxyHgdZLiI1uV6qHwTAq/iYX2fUNCADy9ZHk2gn7wnfyvLqoAPMgRcNmBhN1DCx66/HR0LfY37ddgGcovJYrKBQDTsrbKneV1 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, 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. 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. --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 > > > > > > > >