bcachefs: Some compression improvements

In __bio_map_or_bounce(), the check for if the bio is physically
contiguous is improved; it's now more readable and handles multi page
but contiguous bios.

Also when decompressing, we were doing a redundant memcpy in the case
where we were able to use vmap to map a bio contigiously.

Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

diff --git a/fs/bcachefs/compress.c b/fs/bcachefs/compress.c
index 89eb03a988f181140afeddee5601ad99c5ef124e..41d0b49d354fda0dfd5df2c6d2a24049a0431487 100644 (file)
--- a/fs/bcachefs/compress.c
+++ b/fs/bcachefs/compress.c
@@ -39,6 +39,24 @@ static struct bbuf __bounce_alloc(struct bch_fs *c, unsigned size, int rw)
        BUG();
 }
 
+static bool bio_phys_contig(struct bio *bio, struct bvec_iter start)
+{
+       struct bio_vec bv;
+       struct bvec_iter iter;
+       void *expected_start = NULL;
+
+       __bio_for_each_bvec(bv, bio, iter, start) {
+               if (expected_start &&
+                   expected_start != page_address(bv.bv_page) + bv.bv_offset)
+                       return false;
+
+               expected_start = page_address(bv.bv_page) +
+                       bv.bv_offset + bv.bv_len;
+       }
+
+       return true;
+}
+
 static struct bbuf __bio_map_or_bounce(struct bch_fs *c, struct bio *bio,
                                       struct bvec_iter start, int rw)
 {
@@ -48,27 +66,28 @@ static struct bbuf __bio_map_or_bounce(struct bch_fs *c, struct bio *bio,
        unsigned nr_pages = 0;
        struct page *stack_pages[16];
        struct page **pages = NULL;
-       bool first = true;
-       unsigned prev_end = PAGE_SIZE;
        void *data;
 
        BUG_ON(bvec_iter_sectors(start) > c->sb.encoded_extent_max);
 
-#ifndef CONFIG_HIGHMEM
-       __bio_for_each_bvec(bv, bio, iter, start) {
-               if (bv.bv_len == start.bi_size)
-                       return (struct bbuf) {
-                               .b = page_address(bv.bv_page) + bv.bv_offset,
-                               .type = BB_NONE, .rw = rw
-                       };
-       }
-#endif
+       if (!IS_ENABLED(CONFIG_HIGHMEM) &&
+           bio_phys_contig(bio, start))
+               return (struct bbuf) {
+                       .b = page_address(bio_iter_page(bio, start)) +
+                               bio_iter_offset(bio, start),
+                       .type = BB_NONE, .rw = rw
+               };
+
+       /* check if we can map the pages contiguously: */
        __bio_for_each_segment(bv, bio, iter, start) {
-               if ((!first && bv.bv_offset) ||
-                   prev_end != PAGE_SIZE)
+               if (iter.bi_size != start.bi_size &&
+                   bv.bv_offset)
+                       goto bounce;
+
+               if (bv.bv_len < iter.bi_size &&
+                   bv.bv_offset + bv.bv_len < PAGE_SIZE)
                        goto bounce;
 
-               prev_end = bv.bv_offset + bv.bv_len;
                nr_pages++;
        }
 
@@ -264,7 +283,8 @@ int bch2_bio_uncompress(struct bch_fs *c, struct bio *src,
        if (ret)
                goto err;
 
-       if (dst_data.type != BB_NONE)
+       if (dst_data.type != BB_NONE &&
+           dst_data.type != BB_VMAP)
                memcpy_to_bio(dst, dst_iter, dst_data.b + (crc.offset << 9));
 err:
        bio_unmap_or_unbounce(c, dst_data);
@@ -407,7 +427,8 @@ static unsigned __bio_compress(struct bch_fs *c,
        memset(dst_data.b + *dst_len, 0, pad);
        *dst_len += pad;
 
-       if (dst_data.type != BB_NONE)
+       if (dst_data.type != BB_NONE &&
+           dst_data.type != BB_VMAP)
                memcpy_to_bio(dst, dst->bi_iter, dst_data.b);
 
        BUG_ON(!*dst_len || *dst_len > dst->bi_iter.bi_size);