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SubjectRe: [PATCH v3 9/9] zram: use crypto decompress_noctx API
On Mon, Sep 21, 2015 at 12:51:28PM +0900, Minchan Kim wrote:
> On Fri, Sep 18, 2015 at 02:19:24PM +0900, Joonsoo Kim wrote:
> > Crypto subsystem now supports decompress_noctx API that requires
> > special tfm_noctx. This tfm can be shared by multiple concurrent
> > decompress user because this API doesn't rely on this tfm object
> > except to fetch decompress function pointer.
> >
> > Until changing to use crypto API, zram doesn't require any zstrm
> > on decompress so decompress is parallelized unlimitedly. But, previous
> > patch make zram to use crypto API and this requires one zstrm on every
> > decompress users so, in some zstrm contended situations, zram's
> > performance would be degraded.
> >
> > This patch makes zram use decompress_noctx API and restore zram's
> > performance as the time that zram doesn't use crypto API.
> >
> > Following is zram's read performance number.
> >
> > * iozone -t 4 -R -r 16K -s 60M -I +Z -i 0 -i 1
> > * max_stream is set to 1
> > * Output is in Kbytes/sec
> >
> > zram-base vs zram-crypto vs zram-crypto-noctx
> >
> > Read 10411701.88 6426911.62 9423894.38
> > Re-read 10017386.62 6428218.88 11000063.50
> >
> > Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> > ---
> > drivers/block/zram/zcomp.c | 24 +++++++++++++++++++++++-
> > drivers/block/zram/zcomp.h | 1 +
> > 2 files changed, 24 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/block/zram/zcomp.c b/drivers/block/zram/zcomp.c
> > index c2ed7c8..a020200 100644
> > --- a/drivers/block/zram/zcomp.c
> > +++ b/drivers/block/zram/zcomp.c
> > @@ -319,9 +319,12 @@ void zcomp_compress_end(struct zcomp *comp, struct zcomp_strm *zstrm)
> > zcomp_strm_release(comp, zstrm);
> > }
> >
> > -/* Never return NULL, may sleep */
> > +/* May return NULL, may sleep */
> > struct zcomp_strm *zcomp_decompress_begin(struct zcomp *comp)
> > {
> > + if (comp->tfm_noctx)
> > + return NULL;
>
> Hmm,, I understand why returns NULL but it seems to be awkward to use NULL
> to express meaningful semantic and following functions relies on.
> If I have a time, I will think over.

I also think that it's not good thing but I can't think any better
idea. Please let me know if you have better one.

>
> > +
> > return zcomp_strm_find(comp);
> > }
> >
> > @@ -346,11 +349,18 @@ int zcomp_decompress(struct zcomp *comp, struct zcomp_strm *zstrm,
> > {
> > unsigned int size = PAGE_SIZE;
> >
> > + if (!zstrm) {
> > + return crypto_comp_decompress_noctx(comp->tfm_noctx,
> > + src, src_len, dst, &size);
> > + }
> > +
> > return crypto_comp_decompress(zstrm->tfm, src, src_len, dst, &size);
> > }
> >
> > void zcomp_destroy(struct zcomp *comp)
> > {
> > + if (comp->tfm_noctx)
> > + crypto_free_comp_noctx(comp->tfm_noctx);
> > comp->destroy(comp);
> > kfree(comp);
> > }
> > @@ -366,6 +376,7 @@ struct zcomp *zcomp_create(const char *compress, int max_strm)
> > {
> > struct zcomp *comp;
> > const char *backend;
> > + struct crypto_comp *tfm;
> >
> > backend = find_backend(compress);
> > if (!backend)
> > @@ -384,5 +395,16 @@ struct zcomp *zcomp_create(const char *compress, int max_strm)
> > kfree(comp);
> > return ERR_PTR(-ENOMEM);
> > }
> > +
> > + /*
> > + * Prepare to use crypto decompress_noctx API. One tfm is required
> > + * to initialize crypto algorithm properly and fetch corresponding
> > + * function pointer. But, it is sharable for multiple concurrent
> > + * decompress users.
> > + */
>
> Please comment out that this API will return NULL if the compressor doesn't
> support noctx mode.

Will do.

Thanks.


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