When correcting a data block, the FEC code performs optimally when it has enough buffers to hold all the needed RS blocks. That number of buffers is '1 << (v->data_dev_block_bits - DM_VERITY_FEC_BUF_RS_BITS)'.
However, since v->data_dev_block_bits isn't a compile-time constant, the code actually used PAGE_SHIFT instead. With the traditional PAGE_SIZE == data_block_size == 4096, this was fine. However, when PAGE_SIZE > data_block_size, this wastes space. E.g., with data_block_size == 4096 && PAGE_SIZE == 16384, struct dm_verity_fec_io is 9240 bytes, when in fact only 3096 bytes are needed. Fix this by making dm_verity_fec_io::bufs a variable-length array. This makes the macros DM_VERITY_FEC_BUF_MAX and fec_for_each_extra_buffer() no longer apply, so remove them. Also remove the related macro fec_for_each_prealloc_buffer(), since DM_VERITY_FEC_BUF_PREALLOC is fixed at 1 and was already assumed to be 1 (considering that mempool_alloc() shouldn't be called in a loop). Signed-off-by: Eric Biggers <[email protected]> --- drivers/md/dm-verity-fec.c | 41 ++++++++++++++++++++------------------ drivers/md/dm-verity-fec.h | 14 ++++++++----- 2 files changed, 31 insertions(+), 24 deletions(-) diff --git a/drivers/md/dm-verity-fec.c b/drivers/md/dm-verity-fec.c index bf533ffa7d56..7574e65c32ae 100644 --- a/drivers/md/dm-verity-fec.c +++ b/drivers/md/dm-verity-fec.c @@ -8,10 +8,22 @@ #include "dm-verity-fec.h" #include <linux/math64.h> #define DM_MSG_PREFIX "verity-fec" +/* + * When correcting a data block, the FEC code performs optimally when it can + * collect all the associated RS blocks at the same time. As each byte is part + * of a different RS block, there are '1 << data_dev_block_bits' RS blocks. + * There are '1 << DM_VERITY_FEC_BUF_RS_BITS' RS blocks per buffer, so that + * gives '1 << (data_dev_block_bits - DM_VERITY_FEC_BUF_RS_BITS)' buffers. + */ +static inline unsigned int fec_max_nbufs(struct dm_verity *v) +{ + return 1 << (v->data_dev_block_bits - DM_VERITY_FEC_BUF_RS_BITS); +} + /* * If error correction has been configured, returns true. */ bool verity_fec_is_enabled(struct dm_verity *v) { @@ -57,18 +69,10 @@ static u8 *fec_read_parity(struct dm_verity *v, u64 rsb, int index, } return res; } -/* Loop over each preallocated buffer slot. */ -#define fec_for_each_prealloc_buffer(__i) \ - for (__i = 0; __i < DM_VERITY_FEC_BUF_PREALLOC; __i++) - -/* Loop over each extra buffer slot. */ -#define fec_for_each_extra_buffer(io, __i) \ - for (__i = DM_VERITY_FEC_BUF_PREALLOC; __i < DM_VERITY_FEC_BUF_MAX; __i++) - /* Loop over each allocated buffer. */ #define fec_for_each_buffer(io, __i) \ for (__i = 0; __i < (io)->nbufs; __i++) /* Loop over each RS block in each allocated buffer. */ @@ -305,24 +309,23 @@ static int fec_read_bufs(struct dm_verity *v, struct dm_verity_io *io, * Additional buffers are also allocated opportunistically to improve error * correction performance, but these aren't required to succeed. */ static struct dm_verity_fec_io *fec_alloc_and_init_io(struct dm_verity *v) { + const unsigned int max_nbufs = fec_max_nbufs(v); struct dm_verity_fec *f = v->fec; struct dm_verity_fec_io *fio; unsigned int n; fio = mempool_alloc(&f->fio_pool, GFP_NOIO); fio->rs = mempool_alloc(&f->rs_pool, GFP_NOIO); - memset(fio->bufs, 0, sizeof(fio->bufs)); - - fec_for_each_prealloc_buffer(n) - fio->bufs[n] = mempool_alloc(&f->prealloc_pool, GFP_NOIO); + static_assert(DM_VERITY_FEC_BUF_PREALLOC == 1); + fio->bufs[0] = mempool_alloc(&f->prealloc_pool, GFP_NOIO); /* try to allocate the maximum number of buffers */ - fec_for_each_extra_buffer(fio, n) { + for (n = 1; n < max_nbufs; n++) { fio->bufs[n] = kmem_cache_alloc(f->cache, GFP_NOWAIT); /* we can manage with even one buffer if necessary */ if (unlikely(!fio->bufs[n])) break; } @@ -460,16 +463,15 @@ void __verity_fec_finish_io(struct dm_verity_io *io) struct dm_verity_fec *f = io->v->fec; struct dm_verity_fec_io *fio = io->fec_io; mempool_free(fio->rs, &f->rs_pool); - fec_for_each_prealloc_buffer(n) - mempool_free(fio->bufs[n], &f->prealloc_pool); + static_assert(DM_VERITY_FEC_BUF_PREALLOC == 1); + mempool_free(fio->bufs[0], &f->prealloc_pool); - fec_for_each_extra_buffer(fio, n) - if (fio->bufs[n]) - kmem_cache_free(f->cache, fio->bufs[n]); + for (n = 1; n < fio->nbufs; n++) + kmem_cache_free(f->cache, fio->bufs[n]); mempool_free(fio->output, &f->output_pool); mempool_free(fio, &f->fio_pool); } @@ -732,11 +734,12 @@ int verity_fec_ctr(struct dm_verity *v) return -E2BIG; } /* Preallocate some dm_verity_fec_io structures */ ret = mempool_init_kmalloc_pool(&f->fio_pool, num_online_cpus(), - sizeof(struct dm_verity_fec_io)); + struct_size((struct dm_verity_fec_io *)0, + bufs, fec_max_nbufs(v))); if (ret) { ti->error = "Cannot allocate FEC IO pool"; return ret; } diff --git a/drivers/md/dm-verity-fec.h b/drivers/md/dm-verity-fec.h index b9488d1ddf14..84f8299673ff 100644 --- a/drivers/md/dm-verity-fec.h +++ b/drivers/md/dm-verity-fec.h @@ -17,13 +17,10 @@ #define DM_VERITY_FEC_MIN_RSN 231 /* ~10% space overhead */ /* buffers for deinterleaving and decoding */ #define DM_VERITY_FEC_BUF_PREALLOC 1 /* buffers to preallocate */ #define DM_VERITY_FEC_BUF_RS_BITS 4 /* 1 << RS blocks per buffer */ -/* we need buffers for at most 1 << block size RS blocks */ -#define DM_VERITY_FEC_BUF_MAX \ - (1 << (PAGE_SHIFT - DM_VERITY_FEC_BUF_RS_BITS)) #define DM_VERITY_OPT_FEC_DEV "use_fec_from_device" #define DM_VERITY_OPT_FEC_BLOCKS "fec_blocks" #define DM_VERITY_OPT_FEC_START "fec_start" #define DM_VERITY_OPT_FEC_ROOTS "fec_roots" @@ -50,14 +47,21 @@ struct dm_verity_fec { /* per-bio data */ struct dm_verity_fec_io { struct rs_control *rs; /* Reed-Solomon state */ int erasures[DM_VERITY_FEC_MAX_RSN]; /* erasures for decode_rs8 */ - u8 *bufs[DM_VERITY_FEC_BUF_MAX]; /* bufs for deinterleaving */ - unsigned int nbufs; /* number of buffers allocated */ u8 *output; /* buffer for corrected output */ unsigned int level; /* recursion level */ + unsigned int nbufs; /* number of buffers allocated */ + /* + * Buffers for deinterleaving RS blocks. Each buffer has space for + * the data bytes of (1 << DM_VERITY_FEC_BUF_RS_BITS) RS blocks. The + * array length is fec_max_nbufs(v), and we try to allocate that many + * buffers. However, in low-memory situations we may be unable to + * allocate all buffers. 'nbufs' holds the number actually allocated. + */ + u8 *bufs[]; }; #ifdef CONFIG_DM_VERITY_FEC /* each feature parameter requires a value */ -- 2.52.0
