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Subject[RFC PATCH 10/16] DM: Try to use the bio buffer for decompression instead of allocating one.
Date
The read path allocates a temporary buffer to hold decompressed data, which is
than copied into the caller's bio buffer.

Instead of allocating a temporary buffer to hold the decompressed data,
decompress the data in the caller's bio buffer. This can be done only if the
destination in the bio-buffer is contigious within the same bio-segment.

Signed-off-by: Ram Pai <linuxram@us.ibm.com>
---
drivers/md/dm-inplace-compress.c | 143 ++++++++++++++++++++++++++-----------
drivers/md/dm-inplace-compress.h | 2 +
2 files changed, 102 insertions(+), 43 deletions(-)

diff --git a/drivers/md/dm-inplace-compress.c b/drivers/md/dm-inplace-compress.c
index c56d9b7..f6b95e3 100644
--- a/drivers/md/dm-inplace-compress.c
+++ b/drivers/md/dm-inplace-compress.c
@@ -792,11 +792,34 @@ static void dm_icomp_kfree(void *addr, unsigned int size)
kfree(addr);
}

+static void dm_icomp_release_decomp_buffer(struct dm_icomp_io_range *io)
+{
+ if (!io->decomp_data)
+ return;

-static void dm_icomp_free_io_range(struct dm_icomp_io_range *io)
+ if (io->decomp_kmap)
+ kunmap(io->decomp_real_data);
+ else
+ dm_icomp_kfree(io->decomp_real_data, io->decomp_req_len);
+ io->decomp_data = io->decomp_real_data = NULL;
+ io->decomp_len = 0;
+ io->decomp_kmap = false;
+}
+
+static void dm_icomp_release_comp_buffer(struct dm_icomp_io_range *io)
{
- dm_icomp_kfree(io->decomp_data, io->decomp_len);
+ if (!io->comp_data)
+ return;
dm_icomp_kfree(io->comp_data, io->comp_len);
+
+ io->comp_data = NULL;
+ io->comp_len = 0;
+}
+
+static void dm_icomp_free_io_range(struct dm_icomp_io_range *io)
+{
+ dm_icomp_release_decomp_buffer(io);
+ dm_icomp_release_comp_buffer(io);
kmem_cache_free(dm_icomp_io_range_cachep, io);
}

@@ -890,7 +913,9 @@ static struct dm_icomp_io_range *dm_icomp_create_io_range(
io->req = req;

io->decomp_data = NULL;
+ io->decomp_real_data = NULL;
io->decomp_len = 0;
+ io->decomp_kmap = false;
io->decomp_req_len = 0;
return io;
}
@@ -909,15 +934,43 @@ static struct dm_icomp_io_range *dm_icomp_create_io_read_range(
return io;
}

-static int dm_icomp_update_io_read_range(struct dm_icomp_io_range *io)
+static int dm_icomp_update_io_read_range(struct dm_icomp_io_range *io,
+ struct bio *bio, ssize_t bio_off)
{
+ struct bvec_iter iter;
+ struct bio_vec bv;
+ bool just_use = false;
+
if (io->decomp_len)
return 0;

+ /* use a bio buffer long enough to hold the uncompressed data */
+ bio_for_each_segment(bv, bio, iter) {
+ int avail_len;
+ int length = bv.bv_len;
+
+ if (!just_use && bio_off >= length) {
+ bio_off -= length;
+ continue;
+ }
+ avail_len = just_use ? length : length-bio_off;
+ if (avail_len >= io->decomp_req_len) {
+ io->decomp_real_data = kmap(bv.bv_page);
+ io->decomp_data = io->decomp_real_data + bio_off;
+ io->decomp_len = io->decomp_req_len = avail_len;
+ io->decomp_kmap = true;
+ return 0;
+ }
+ just_use = true;
+ }
+
+ /* none available. :( Allocate one */
io->decomp_data = dm_icomp_kmalloc(io->decomp_req_len, GFP_NOIO);
if (!io->decomp_data)
return 1;
+ io->decomp_real_data = io->decomp_data;
io->decomp_len = io->decomp_req_len;
+ io->decomp_kmap = false;

return 0;
}
@@ -978,24 +1031,34 @@ static struct dm_icomp_io_range *dm_icomp_create_io_write_range(
struct dm_icomp_req *req)
{
struct dm_icomp_io_range *io;
+ struct bio *bio = req->bio;
sector_t size = bio_sectors(req->bio)<<9;
+ int segments = bio_segments(bio);
int comp_len = dm_icomp_compressor_len(req->info, size);
void *addr;

- addr = dm_icomp_kmalloc(size, GFP_NOIO);
+ if (segments == 1) {
+ struct bio_vec bv = bio_iovec(bio);
+
+ addr = kmap(bv.bv_page);
+ } else
+ addr = dm_icomp_kmalloc(size, GFP_NOIO);
+
if (!addr)
return NULL;

io = dm_icomp_create_io_range(req, comp_len);
if (!io) {
- dm_icomp_kfree(addr, size);
+ (segments == 1) ? kunmap(addr) : dm_icomp_kfree(addr, size);
return NULL;
}

- io->decomp_data = addr;
+ io->decomp_data = io->decomp_real_data = addr;
io->decomp_len = size;

- dm_icomp_bio_copy(req->bio, 0, io->decomp_data, size, true);
+ io->decomp_kmap = (segments == 1);
+ if (!io->decomp_kmap)
+ dm_icomp_bio_copy(req->bio, 0, io->decomp_data, size, true);
return io;
}

@@ -1105,7 +1168,15 @@ static void dm_icomp_handle_read_decomp(struct dm_icomp_req *req)

io->io_region.sector -= req->info->data_start;

- if (dm_icomp_update_io_read_range(io)) {
+ if (io->io_region.sector >=
+ req->bio->bi_iter.bi_sector)
+ dst_off = (io->io_region.sector -
+ req->bio->bi_iter.bi_sector) << 9;
+ else
+ src_off = (req->bio->bi_iter.bi_sector -
+ io->io_region.sector) << 9;
+
+ if (dm_icomp_update_io_read_range(io, req->bio, dst_off)) {
req->result = -EIO;
return;
}
@@ -1114,20 +1185,19 @@ static void dm_icomp_handle_read_decomp(struct dm_icomp_req *req)
ret = dm_icomp_io_range_decompress(req->info, io->comp_data,
io->comp_len, io->decomp_data, io->decomp_len);
if (ret < 0) {
+ dm_icomp_release_decomp_buffer(io);
+ dm_icomp_release_comp_buffer(io);
req->result = -EIO;
return;
}

- if (io->io_region.sector >= req->bio->bi_iter.bi_sector)
- dst_off = (io->io_region.sector -
- req->bio->bi_iter.bi_sector) << 9;
- else
- src_off = (req->bio->bi_iter.bi_sector -
- io->io_region.sector) << 9;
-
len = min_t(ssize_t, io->decomp_len - src_off,
(bio_sectors(req->bio) << 9) - dst_off);

+ dm_icomp_bio_copy(req->bio, dst_off,
+ ((ret == 1) ? io->comp_data : io->decomp_data) + src_off,
+ len, false);
+
/* io range in all_io list is ordered for read IO */
while (bio_off != dst_off) {
ssize_t size = min_t(ssize_t, PAGE_SIZE,
@@ -1137,13 +1207,9 @@ static void dm_icomp_handle_read_decomp(struct dm_icomp_req *req)
bio_off += size;
}

- if (ret == 1)
- dm_icomp_bio_copy(req->bio, dst_off,
- io->comp_data + src_off, len, false);
- else
- dm_icomp_bio_copy(req->bio, dst_off,
- io->decomp_data + src_off, len, false);
bio_off = dst_off + len;
+ dm_icomp_release_decomp_buffer(io);
+ dm_icomp_release_comp_buffer(io);
}

while (bio_off != (bio_sectors(req->bio) << 9)) {
@@ -1270,29 +1336,20 @@ static int dm_icomp_handle_write_modify(struct dm_icomp_io_range *io,
if (start < req->bio->bi_iter.bi_sector && start + count >
bio_end_sector(req->bio)) {
/* we don't split an extent */
- if (ret == 1) {
- memcpy(io->decomp_data, io->comp_data, io->decomp_len);
- dm_icomp_bio_copy(req->bio, 0,
- io->decomp_data +
- ((req->bio->bi_iter.bi_sector - start) << 9),
- bio_sectors(req->bio) << 9, true);
- } else {
- dm_icomp_bio_copy(req->bio, 0,
- io->decomp_data +
- ((req->bio->bi_iter.bi_sector - start) << 9),
- bio_sectors(req->bio) << 9, true);
-
- dm_icomp_kfree(io->comp_data, io->comp_len);
- /* New compressed len might be bigger */
- io->comp_data = dm_icomp_kmalloc(
- dm_icomp_compressor_len(
- req->info, io->decomp_len), GFP_NOIO);
- io->comp_len = io->decomp_len;
- if (!io->comp_data) {
- req->result = -ENOMEM;
- return -EIO;
+ if (!io->decomp_kmap) {
+ if (ret == 1) {
+ memcpy(io->decomp_data, io->comp_data,
+ io->decomp_len);
+ dm_icomp_bio_copy(req->bio, 0,
+ io->decomp_data +
+ ((req->bio->bi_iter.bi_sector - start) << 9),
+ bio_sectors(req->bio) << 9, true);
+ } else {
+ dm_icomp_bio_copy(req->bio, 0,
+ io->decomp_data +
+ ((req->bio->bi_iter.bi_sector - start) << 9),
+ bio_sectors(req->bio) << 9, true);
}
- io->io_req.mem.ptr.addr = io->comp_data;
}
/* need compress data */
ret = 0;
diff --git a/drivers/md/dm-inplace-compress.h b/drivers/md/dm-inplace-compress.h
index d9cf05a..e144e96 100644
--- a/drivers/md/dm-inplace-compress.h
+++ b/drivers/md/dm-inplace-compress.h
@@ -115,7 +115,9 @@ struct dm_icomp_meta_io {
struct dm_icomp_io_range {
struct dm_io_request io_req;
struct dm_io_region io_region;
+ int decomp_kmap; /* Is the decomp_data kmapped'? */
void *decomp_data;
+ void *decomp_real_data; /* holds the actual start of the buffer */
unsigned int decomp_req_len;/* originally requested length */
unsigned int decomp_len; /* actual allocated/mapped length */
void *comp_data;
--
1.7.1
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