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dm-verity: make dm_verity_fec_io::bufs variable-length

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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.  For
consistency, and because 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), also remove the related macros
DM_VERITY_FEC_BUF_PREALLOC and fec_for_each_prealloc_buffer().

Signed-off-by: Eric Biggers <ebiggers@kernel.org>
Reviewed-by: Sami Tolvanen <samitolvanen@google.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
This commit is contained in:
Eric Biggers
2025-12-19 11:29:04 -08:00
committed by Mikulas Patocka
parent b140a921ea
commit 533e641b45
2 changed files with 31 additions and 28 deletions
Download Patch File Download Diff File Expand all files Collapse all files

44
drivers/md/dm-verity-fec.c
View File

@@ -10,6 +10,18 @@
#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.
*/
@@ -59,14 +71,6 @@ 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++)
@@ -307,6 +311,7 @@ static int fec_read_bufs(struct dm_verity *v, struct dm_verity_io *io,
*/
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;
@@ -314,13 +319,10 @@ static struct dm_verity_fec_io *fec_alloc_and_init_io(struct dm_verity *v)
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);
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]))
@@ -462,12 +464,10 @@ void __verity_fec_finish_io(struct dm_verity_io *io)
mempool_free(fio->rs, &f->rs_pool);
fec_for_each_prealloc_buffer(n)
mempool_free(fio->bufs[n], &f->prealloc_pool);
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);
@@ -735,7 +735,8 @@ int verity_fec_ctr(struct dm_verity *v)
/* 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;
@@ -757,9 +758,8 @@ int verity_fec_ctr(struct dm_verity *v)
return -ENOMEM;
}
/* Preallocate DM_VERITY_FEC_BUF_PREALLOC buffers for each thread */
ret = mempool_init_slab_pool(&f->prealloc_pool, num_online_cpus() *
DM_VERITY_FEC_BUF_PREALLOC,
/* Preallocate one buffer for each thread */
ret = mempool_init_slab_pool(&f->prealloc_pool, num_online_cpus(),
f->cache);
if (ret) {
ti->error = "Cannot allocate FEC buffer prealloc pool";

15
drivers/md/dm-verity-fec.h
View File

@@ -17,11 +17,7 @@
#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"
@@ -52,10 +48,17 @@ struct dm_verity_fec {
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