On 2023/2/20 16:53, Geert Uytterhoeven wrote:
Hi Qu,
On Tue, 7 Feb 2023, Qu Wenruo wrote:
In btrfs_io_context structure, we have a pointer raid_map, which is to
indicate the logical bytenr for each stripe.
But considering we always call sort_parity_stripes(), the result
raid_map[] is always sorted, thus raid_map[0] is always the logical
bytenr of the full stripe.
So why we waste the space and time (for sorting) for raid_map[]?
This patch will replace btrfs_io_context::raid_map with a single u64
number, full_stripe_start, by:
- Replace btrfs_io_context::raid_map with full_stripe_start
- Replace call sites using raid_map[0] to use full_stripe_start
- Replace call sites using raid_map[i] to compare with nr_data_stripes.
The benefits are:
- Less memory wasted on raid_map
It's sizeof(u64) * num_stripes vs size(u64).
It's always a save for at least one u64, and the benefit grows larger
with num_stripes.
- No more weird alloc_btrfs_io_context() behavior
As there is only one fixed size + one variable length array.
Signed-off-by: Qu Wenruo <wqu@xxxxxxxx>
Thanks for your patch, which is now commit 4a8c6e8a6dc8ae4c ("btrfs:
replace btrfs_io_context::raid_map with a fixed u64 value") in
next-20230220.
noreply@xxxxxxxxxxxxxx reported several build failures when
building for 32-bit platforms:
ERROR: modpost: "__umoddi3" [fs/btrfs/btrfs.ko] undefined!
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -6556,35 +6532,44 @@ int __btrfs_map_block(struct btrfs_fs_info
*fs_info, enum btrfs_map_op op,
}
bioc->map_type = map->type;
- for (i = 0; i < num_stripes; i++) {
- set_io_stripe(&bioc->stripes[i], map, stripe_index,
stripe_offset,
- stripe_nr);
- stripe_index++;
- }
-
- /* Build raid_map */
+ /*
+ * For RAID56 full map, we need to make sure the stripes[] follows
+ * the rule that data stripes are all ordered, then followed with P
+ * and Q (if we have).
+ *
+ * It's still mostly the same as other profiles, just with extra
+ * rotataion.
+ */
if (map->type & BTRFS_BLOCK_GROUP_RAID56_MASK && need_raid_map &&
(need_full_stripe(op) || mirror_num > 1)) {
- u64 tmp;
- unsigned rot;
-
- /* Work out the disk rotation on this stripe-set */
- rot = stripe_nr % num_stripes;
-
- /* Fill in the logical address of each stripe */
- tmp = stripe_nr * data_stripes;
- for (i = 0; i < data_stripes; i++)
- bioc->raid_map[(i + rot) % num_stripes] =
- em->start + ((tmp + i) << BTRFS_STRIPE_LEN_SHIFT);
-
- bioc->raid_map[(i + rot) % map->num_stripes] = RAID5_P_STRIPE;
- if (map->type & BTRFS_BLOCK_GROUP_RAID6)
- bioc->raid_map[(i + rot + 1) % num_stripes] =
- RAID6_Q_STRIPE;
-
- sort_parity_stripes(bioc, num_stripes);
+ /*
+ * For RAID56 @stripe_nr is already the number of full stripes
+ * before us, which is also the rotation value (needs to modulo
+ * with num_stripes).
+ *
+ * In this case, we just add @stripe_nr with @i, then do the
+ * modulo, to reduce one modulo call.
+ */
+ bioc->full_stripe_logical = em->start +
+ ((stripe_nr * data_stripes) << BTRFS_STRIPE_LEN_SHIFT);
+ for (i = 0; i < num_stripes; i++) {
+ set_io_stripe(&bioc->stripes[i], map,
+ (i + stripe_nr) % num_stripes,
As stripe_nr is u64, this is a 64-by-32 modulo operation, which
should be implemented using a helper from include/linux/math64.h
instead.
This is an older version, in the latest version, the @stripe_nr variable
is also u32, and I tried compiling the latest branch with i686, it
doesn't cause any u64 division problems anymore.
You can find the latest branch in either github or from the mailling list:
https://github.com/adam900710/linux/tree/map_block_refactor
https://lore.kernel.org/linux-btrfs/cover.1676611535.git.wqu@xxxxxxxx/
Thanks,
Qu
+ stripe_offset, stripe_nr);
+ }
+ } else {
+ /*
+ * For all other non-RAID56 profiles, just copy the target
+ * stripe into the bioc.
+ */
+ for (i = 0; i < num_stripes; i++) {
+ set_io_stripe(&bioc->stripes[i], map, stripe_index,
+ stripe_offset, stripe_nr);
+ stripe_index++;
+ }
}
+
if (need_full_stripe(op))
max_errors = btrfs_chunk_max_errors(map);
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 --
geert@xxxxxxxxxxxxxx
In personal conversations with technical people, I call myself a hacker.
But
when I'm talking to journalists I just say "programmer" or something
like that.
-- Linus Torvalds
