On Tue, May 19, 2015 at 01:49:45PM +0800, Herbert Xu wrote:

On Mon, May 18, 2015 at 10:46:56PM -0700, Jaegeuk Kim wrote:

quoted

This patch adds a parameter, gfp_t, for __crypto_alloc_tfm.
Now EXT4 and F2FS use the crypto engine to encrypt a page when writing it to the
disk.
That happens during ->writepage and it needs to allocate memory with
GFP_NOFS.

Otherwise, in the f2fs case, kernel reports such the following warning.

Normally crypto structures should only be allocated on control
paths where sleeping or swapping is not an issue.  Why is ext4
doing crypto allocations on the data path?

Recently, Ted introduced per-file encryption feature as follows.

https://lwn.net/Articles/639427/

The call path in fs/ext4/crypto.c is:
 - writepage
  - ext4_encrypt
   - ext4_get_crypto_ctx
    - crypto_alloc_ablkcipher

AFAIK, this way can achieve to reduce memory footprint gracefully.
Just before submitting bios, fs allocates the required memory, and then end_io
will free them in pair.

Thanks,

Cheers,
-- 
Email: Herbert Xu [off-list ref]
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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