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    SubjectRe: [PATCH v3 9/9] zram: use crypto decompress_noctx API
    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.

    > +
    > 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.

    Thanks.


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