Re: [PATCHv7 3/7] zram: factor out single stream compression

Sergey Senozhatsky
2014-02-26T11:36:22Z

Hello Minchan,

On (02/26/14 13:34), Minchan Kim wrote:
> Hello Sergey,
>
> On Tue, Feb 25, 2014 at 02:34:29PM +0300, Sergey Senozhatsky wrote:
> > This is preparation patch to add multi stream support to zcomp.
> >
> > Introduce struct zcomp_strm_single and a set of functions to manage zcomp_strm
> > stream access. zcomp_strm_single implements single compession stream, same way
> > as current zcomp implementation. This moves zcomp_strm stream control and
> > locking from zcomp, so compressing backend zcomp is not aware of required
> > locking (single and multi streams require different locking schemes).
>
> Please, add why we need different locking scheme in here so that
> some people understand why we need this via git log in future.
>

addressed all of your notes, nitpicks and concerns in v8. thanks.

-ss

> >
> > The following set of functions added:
> > - zcomp_strm_single_get()/zcomp_strm_single_put()
> > get and put compression stream, implement required locking
> > - zcomp_strm_single_create()/zcomp_strm_single_destroy()
> > create and destroy zcomp_strm_single
> >
> > New ->strm_get() and ->strm_put() callbacks added to zcomp, which are set to
> > zcomp_strm_single_get() and zcomp_strm_single_put() during initialisation.
> > Instead of direct locking and zcomp_strm access from zcomp_strm_get() and
> > zcomp_strm_put(), zcomp now calls ->strm_get() and ->strm_put()
> > correspondingly.
> >
> > Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
> > ---
> > drivers/block/zram/zcomp.c | 65 +++++++++++++++++++++++++++++++++++++++-------
> > drivers/block/zram/zcomp.h | 7 +++--
> > 2 files changed, 61 insertions(+), 11 deletions(-)
> >
> > diff --git a/drivers/block/zram/zcomp.c b/drivers/block/zram/zcomp.c
> > index 947efe3..e20054b 100644
> > --- a/drivers/block/zram/zcomp.c
> > +++ b/drivers/block/zram/zcomp.c
> > @@ -15,6 +15,14 @@
> >
> > #include "zcomp.h"
> >
> > +/*
> > + * single zcomp_strm backend
> > + */
> > +struct zcomp_strm_single {
> > + struct mutex strm_lock;
> > + struct zcomp_strm *zstrm;
> > +};
> > +
> > extern struct zcomp_backend zcomp_lzo;
> >
> > static struct zcomp_backend *find_backend(const char *compress)
> > @@ -55,17 +63,58 @@ static struct zcomp_strm *zcomp_strm_alloc(struct zcomp *comp)
> > return zstrm;
> > }
> >
> > +static struct zcomp_strm *zcomp_strm_single_get(struct zcomp *comp)
> > +{
> > + struct zcomp_strm_single *zs = comp->stream;
> > + mutex_lock(&zs->strm_lock);
> > + return zs->zstrm;
> > +}
> > +
> > +static void zcomp_strm_single_put(struct zcomp *comp, struct zcomp_strm *zstrm)
> > +{
> > + struct zcomp_strm_single *zs = comp->stream;
> > + mutex_unlock(&zs->strm_lock);
> > +}
> > +
> > +static void zcomp_strm_single_destroy(struct zcomp *comp)
> > +{
> > + struct zcomp_strm_single *zs = comp->stream;
> > + zcomp_strm_free(comp, zs->zstrm);
> > + kfree(zs);
> > +}
> > +
> > +static int zcomp_strm_single_create(struct zcomp *comp)
> > +{
> > + struct zcomp_strm_single *zs;
> > +
> > + comp->destroy = zcomp_strm_single_destroy;
> > + comp->strm_get = zcomp_strm_single_get;
> > + comp->strm_put = zcomp_strm_single_put;
> > + zs = kmalloc(sizeof(struct zcomp_strm_single), GFP_KERNEL);
> > + comp->stream = zs;
> > + if (!zs)
> > + return -ENOMEM;
>
> Firstly check zs nullness and then assign zs to the comp->stream.
> Yeb. your code doesn't have any problem but let's follow normal
> convention.
>
> > +
> > + mutex_init(&zs->strm_lock);
> > + zs->zstrm = zcomp_strm_alloc(comp);
> > + if (!zs->zstrm) {
> > + zcomp_strm_single_destroy(comp);
>
> Let's just call kfree in here instead of xxx_destroy.
> such pair function call is more clear to me rather than using wrapping
> function.
>
>
> > + return -ENOMEM;
> > + }
> > + return 0;
> > +}
> > +
> > struct zcomp_strm *zcomp_strm_get(struct zcomp *comp)
> > {
> > - mutex_lock(&comp->strm_lock);
> > - return comp->zstrm;
> > + return comp->strm_get(comp);
> > }
> >
> > void zcomp_strm_put(struct zcomp *comp, struct zcomp_strm *zstrm)
> > {
> > - mutex_unlock(&comp->strm_lock);
> > + comp->strm_put(comp, zstrm);
> > }
> >
> > +/* compress page */
>
> Function name is clear so I think we don't need a comment.
> If we need such comment, it should introduce previous patches, not this one.
>
> > int zcomp_compress(struct zcomp *comp, struct zcomp_strm *zstrm,
> > const unsigned char *src, size_t *dst_len)
> > {
> > @@ -73,6 +122,7 @@ int zcomp_compress(struct zcomp *comp, struct zcomp_strm *zstrm,
> > zstrm->private);
> > }
> >
> > +/* decompress page */
> > int zcomp_decompress(struct zcomp *comp, const unsigned char *src,
> > size_t src_len, unsigned char *dst)
> > {
> > @@ -81,7 +131,7 @@ int zcomp_decompress(struct zcomp *comp, const unsigned char *src,
> >
> > void zcomp_destroy(struct zcomp *comp)
> > {
> > - zcomp_strm_free(comp, comp->zstrm);
> > + comp->destroy(comp);
> > kfree(comp);
> > }
> >
> > @@ -105,11 +155,8 @@ struct zcomp *zcomp_create(const char *compress)
> > return NULL;
> >
> > comp->backend = backend;
> > - mutex_init(&comp->strm_lock);
> > -
> > - comp->zstrm = zcomp_strm_alloc(comp);
> > - if (!comp->zstrm) {
> > - kfree(comp);
> > + if (zcomp_strm_single_create(comp) != 0) {
> > + zcomp_destroy(comp);
>
> Let's use just kfree.
> If zcomp_strm_single_create fails, it should tidy up all memory
> allocated by itself so caller should just free thing allocate by
> itself.
>
> > return NULL;
> > }
> > return comp;
> > diff --git a/drivers/block/zram/zcomp.h b/drivers/block/zram/zcomp.h
> > index 5106f8e..861e04d 100644
> > --- a/drivers/block/zram/zcomp.h
> > +++ b/drivers/block/zram/zcomp.h
> > @@ -34,9 +34,12 @@ struct zcomp_backend {
> >
> > /* dynamic per-device compression frontend */
> > struct zcomp {
> > - struct mutex strm_lock;
> > - struct zcomp_strm *zstrm;
> > + void *stream;
> > struct zcomp_backend *backend;
> > +
> > + struct zcomp_strm *(*strm_get)(struct zcomp *comp);
> > + void (*strm_put)(struct zcomp *comp, struct zcomp_strm *zstrm);
> > + void (*destroy)(struct zcomp *comp);
> > };
> >
> > struct zcomp *zcomp_create(const char *comp);
> > --
> > 1.9.0.291.g027825b
> >
> > --
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>
> --
> Kind regards,
> Minchan Kim
>