Messages in this thread | | | Date | Mon, 20 Feb 2023 19:50:37 +0800 | Subject | Re: [PATCH v2 4/4] btrfs: replace btrfs_io_context::raid_map[] with a fixed u64 value | From | Qu Wenruo <> |
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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@suse.com> > > 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@ellerman.id.au 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@suse.com/
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@linux-m68k.org > > 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
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