fscrypt: optimize fscrypt_zeroout_range()

Currently fscrypt_zeroout_range() issues and waits on a bio for each
block it writes, which makes it very slow.

Optimize it to write up to 16 pages at a time instead.

Also add a function comment, and improve reliability by allowing the
allocations of the bio and the first ciphertext page to wait on the
corresponding mempools.

Link: https://lore.kernel.org/r/20191226160813.53182-1-ebiggers@kernel.org
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Eric Biggers <ebiggers@google.com>

diff --git a/fs/crypto/bio.c b/fs/crypto/bio.c
index b88d417..4fa18ff 100644 (file)
--- a/fs/crypto/bio.c
+++ b/fs/crypto/bio.c
@@ -41,51 +41,101 @@ void fscrypt_decrypt_bio(struct bio *bio)
 }
 EXPORT_SYMBOL(fscrypt_decrypt_bio);
 
+/**
+ * fscrypt_zeroout_range() - zero out a range of blocks in an encrypted file
+ * @inode: the file's inode
+ * @lblk: the first file logical block to zero out
+ * @pblk: the first filesystem physical block to zero out
+ * @len: number of blocks to zero out
+ *
+ * Zero out filesystem blocks in an encrypted regular file on-disk, i.e. write
+ * ciphertext blocks which decrypt to the all-zeroes block.  The blocks must be
+ * both logically and physically contiguous.  It's also assumed that the
+ * filesystem only uses a single block device, ->s_bdev.
+ *
+ * Note that since each block uses a different IV, this involves writing a
+ * different ciphertext to each block; we can't simply reuse the same one.
+ *
+ * Return: 0 on success; -errno on failure.
+ */
 int fscrypt_zeroout_range(const struct inode *inode, pgoff_t lblk,
-                               sector_t pblk, unsigned int len)
+                         sector_t pblk, unsigned int len)
 {
        const unsigned int blockbits = inode->i_blkbits;
        const unsigned int blocksize = 1 << blockbits;
-       struct page *ciphertext_page;
+       const unsigned int blocks_per_page_bits = PAGE_SHIFT - blockbits;
+       const unsigned int blocks_per_page = 1 << blocks_per_page_bits;
+       struct page *pages[16]; /* write up to 16 pages at a time */
+       unsigned int nr_pages;
+       unsigned int i;
+       unsigned int offset;
        struct bio *bio;
-       int ret, err = 0;
+       int ret, err;
 
-       ciphertext_page = fscrypt_alloc_bounce_page(GFP_NOWAIT);
-       if (!ciphertext_page)
-               return -ENOMEM;
+       if (len == 0)
+               return 0;
 
-       while (len--) {
-               err = fscrypt_crypt_block(inode, FS_ENCRYPT, lblk,
-                                         ZERO_PAGE(0), ciphertext_page,
-                                         blocksize, 0, GFP_NOFS);
-               if (err)
-                       goto errout;
+       BUILD_BUG_ON(ARRAY_SIZE(pages) > BIO_MAX_PAGES);
+       nr_pages = min_t(unsigned int, ARRAY_SIZE(pages),
+                        (len + blocks_per_page - 1) >> blocks_per_page_bits);
 
-               bio = bio_alloc(GFP_NOWAIT, 1);
-               if (!bio) {
-                       err = -ENOMEM;
-                       goto errout;
-               }
+       /*
+        * We need at least one page for ciphertext.  Allocate the first one
+        * from a mempool, with __GFP_DIRECT_RECLAIM set so that it can't fail.
+        *
+        * Any additional page allocations are allowed to fail, as they only
+        * help performance, and waiting on the mempool for them could deadlock.
+        */
+       for (i = 0; i < nr_pages; i++) {
+               pages[i] = fscrypt_alloc_bounce_page(i == 0 ? GFP_NOFS :
+                                                    GFP_NOWAIT | __GFP_NOWARN);
+               if (!pages[i])
+                       break;
+       }
+       nr_pages = i;
+       if (WARN_ON(nr_pages <= 0))
+               return -EINVAL;
+
+       /* This always succeeds since __GFP_DIRECT_RECLAIM is set. */
+       bio = bio_alloc(GFP_NOFS, nr_pages);
+
+       do {
                bio_set_dev(bio, inode->i_sb->s_bdev);
                bio->bi_iter.bi_sector = pblk << (blockbits - 9);
                bio_set_op_attrs(bio, REQ_OP_WRITE, 0);
-               ret = bio_add_page(bio, ciphertext_page, blocksize, 0);
-               if (WARN_ON(ret != blocksize)) {
-                       /* should never happen! */
-                       bio_put(bio);
-                       err = -EIO;
-                       goto errout;
-               }
+
+               i = 0;
+               offset = 0;
+               do {
+                       err = fscrypt_crypt_block(inode, FS_ENCRYPT, lblk,
+                                                 ZERO_PAGE(0), pages[i],
+                                                 blocksize, offset, GFP_NOFS);
+                       if (err)
+                               goto out;
+                       lblk++;
+                       pblk++;
+                       len--;
+                       offset += blocksize;
+                       if (offset == PAGE_SIZE || len == 0) {
+                               ret = bio_add_page(bio, pages[i++], offset, 0);
+                               if (WARN_ON(ret != offset)) {
+                                       err = -EIO;
+                                       goto out;
+                               }
+                               offset = 0;
+                       }
+               } while (i != nr_pages && len != 0);
+
                err = submit_bio_wait(bio);
-               bio_put(bio);
                if (err)
-                       goto errout;
-               lblk++;
-               pblk++;
-       }
+                       goto out;
+               bio_reset(bio);
+       } while (len != 0);
        err = 0;
-errout:
-       fscrypt_free_bounce_page(ciphertext_page);
+out:
+       bio_put(bio);
+       for (i = 0; i < nr_pages; i++)
+               fscrypt_free_bounce_page(pages[i]);
        return err;
 }
 EXPORT_SYMBOL(fscrypt_zeroout_range);