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Message-Id: <20191226160813.53182-1-ebiggers@kernel.org>
Date: Thu, 26 Dec 2019 10:08:13 -0600
From: Eric Biggers <ebiggers@...nel.org>
To: linux-fscrypt@...r.kernel.org
Cc: linux-ext4@...r.kernel.org
Subject: [PATCH] fscrypt: optimize fscrypt_zeroout_range()
From: Eric Biggers <ebiggers@...gle.com>
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.
Signed-off-by: Eric Biggers <ebiggers@...gle.com>
---
fs/crypto/bio.c | 112 ++++++++++++++++++++++++++++++++++--------------
1 file changed, 81 insertions(+), 31 deletions(-)
diff --git a/fs/crypto/bio.c b/fs/crypto/bio.c
index b88d417e186e..4fa18fff9c4e 100644
--- 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);
--
2.24.1
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