Re: [PATCH] crypto: scompress - eliminate percpu scratch buffers

On Fri, Jul 21, 2017 at 02:09:39PM +0100, Ard Biesheuvel wrote:

Right. And is req->dst guaranteed to be assigned in that case? Because
crypto_scomp_sg_alloc() happily allocates pages and kmalloc()s the
scatterlist if req->dst == NULL.

Is there any way we could make these scratch buffers part of the
request structure instead? Or at least defer allocating them until the
first call to crypto_scomp_init_tfm()? And on top of that, we should
probably only use the per-CPU scratch buffers if
CRYPTO_TFM_REQ_MAY_SLEEP is cleared, because in that case, we are not
pre-emptible to begin with, and the concern does not apply.

Well for now scomp is new code so nothing actually uses it.  But
the idea is to convert IPcomp over to acomp and scomp will fill in
as the compatibility glue.

The medium/long-term plan is to convert IPcomp over to a partial
decompression model so that we can allocate pages instead of a
contiguous chunk as we do now.

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