dm-verity: move dm_verity_fec_io to mempool

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Currently, struct dm_verity_fec_io is allocated in the front padding of
struct bio using dm_target::per_io_data_size.  Unfortunately, struct
dm_verity_fec_io is very large: 3096 bytes when CONFIG_64BIT=y &&
PAGE_SIZE == 4096, or 9240 bytes when CONFIG_64BIT=y && PAGE_SIZE ==
16384.  This makes the bio size very large.

Moreover, most of dm_verity_fec_io gets iterated over up to three times,
even on I/O requests that don't require any error correction:

1. To zero the memory on allocation, if init_on_alloc=1.  (This happens
   when the bio is allocated, not in dm-verity itself.)

2. To zero the buffers array in verity_fec_init_io().

3. To free the buffers in verity_fec_finish_io().

Fix all of these inefficiencies by moving dm_verity_fec_io to a mempool.
Replace the embedded dm_verity_fec_io with a pointer
dm_verity_io::fec_io.  verity_fec_init_io() initializes it to NULL,
verity_fec_decode() allocates it on the first call, and
verity_fec_finish_io() cleans it up.  The normal case is that the
pointer simply stays NULL, so the overhead becomes negligible.

Reviewed-by: Sami Tolvanen <samitolvanen@google.com>
Signed-off-by: Eric Biggers <ebiggers@kernel.org>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>

...

This commit is contained in:

Eric Biggers 2025-12-19 11:29:03 -08:00 • committed by Mikulas Patocka

parent a23cc8257e

commit b140a921ea

3 changed files with 54 additions and 60 deletions

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96

drivers/md/dm-verity-fec.c

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14

drivers/md/dm-verity-fec.h

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4

drivers/md/dm-verity.h

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