linux-ext4 - Re: [PATCH] crypto: allow to assign gfp_t for __crypto_alloc

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Date:	Mon, 18 May 2015 23:24:30 -0700
From:	Jaegeuk Kim <jaegeuk@...nel.org>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	davem@...emloft.net, linux-crypto@...r.kernel.org,
	linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-f2fs-devel@...ts.sourceforge.net, ecryptfs@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] crypto: allow to assign gfp_t for __crypto_alloc_tfm

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:
> > 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 <herbert@...dor.apana.org.au>
> Home Page: http://gondor.apana.org.au/~herbert/
> PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
> --
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