Re: [RFC 1/3] zsmalloc: move pages_allocated to zs_pool

[Sergey Senozhatsky <sergey.senozhatsky@gmail.com>]

On (08/13/14 09:59), Dan Streetman wrote:
> On Tue, Aug 5, 2014 at 4:02 AM, Minchan Kim <minchan@kernel.org> wrote:
> > Pages_allocated has counted in size_class structure and when user
> > want to see total_size_bytes, it gathers all of value from each
> > size_class to report the sum.
> >
> > It's not bad if user don't see the value often but if user start
> > to see the value frequently, it would be not a good deal for
> > performance POV.
> >
> > This patch moves the variable from size_class to zs_pool so it would
> > reduce memory footprint (from [255 * 8byte] to [sizeof(atomic_t)])
> > but it adds new locking overhead but it wouldn't be severe because
> > it's not a hot path in zs_malloc(ie, it is called only when new
> > zspage is created, not a object).
> 
> Would using an atomic64_t without locking be simpler?

it would be racy.

	-ss

> 
> >
> > Signed-off-by: Minchan Kim <minchan@kernel.org>
> > ---
> >  mm/zsmalloc.c | 30 ++++++++++++++++--------------
> >  1 file changed, 16 insertions(+), 14 deletions(-)
> >
> > diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> > index fe78189624cf..a6089bd26621 100644
> > --- a/mm/zsmalloc.c
> > +++ b/mm/zsmalloc.c
> > @@ -198,9 +198,6 @@ struct size_class {
> >
> >         spinlock_t lock;
> >
> > -       /* stats */
> > -       u64 pages_allocated;
> > -
> >         struct page *fullness_list[_ZS_NR_FULLNESS_GROUPS];
> >  };
> >
> > @@ -216,9 +213,12 @@ struct link_free {
> >  };
> >
> >  struct zs_pool {
> > +       spinlock_t stat_lock;
> > +
> >         struct size_class size_class[ZS_SIZE_CLASSES];
> >
> >         gfp_t flags;    /* allocation flags used when growing pool */
> > +       unsigned long pages_allocated;
> >  };
> >
> >  /*
> > @@ -882,6 +882,7 @@ struct zs_pool *zs_create_pool(gfp_t flags)
> >
> >         }
> >
> > +       spin_lock_init(&pool->stat_lock);
> >         pool->flags = flags;
> >
> >         return pool;
> > @@ -943,8 +944,10 @@ unsigned long zs_malloc(struct zs_pool *pool, size_t size)
> >                         return 0;
> >
> >                 set_zspage_mapping(first_page, class->index, ZS_EMPTY);
> > +               spin_lock(&pool->stat_lock);
> > +               pool->pages_allocated += class->pages_per_zspage;
> > +               spin_unlock(&pool->stat_lock);
> >                 spin_lock(&class->lock);
> > -               class->pages_allocated += class->pages_per_zspage;
> >         }
> >
> >         obj = (unsigned long)first_page->freelist;
> > @@ -997,14 +1000,14 @@ void zs_free(struct zs_pool *pool, unsigned long obj)
> >
> >         first_page->inuse--;
> >         fullness = fix_fullness_group(pool, first_page);
> > -
> > -       if (fullness == ZS_EMPTY)
> > -               class->pages_allocated -= class->pages_per_zspage;
> > -
> >         spin_unlock(&class->lock);
> >
> > -       if (fullness == ZS_EMPTY)
> > +       if (fullness == ZS_EMPTY) {
> > +               spin_lock(&pool->stat_lock);
> > +               pool->pages_allocated -= class->pages_per_zspage;
> > +               spin_unlock(&pool->stat_lock);
> >                 free_zspage(first_page);
> > +       }
> >  }
> >  EXPORT_SYMBOL_GPL(zs_free);
> >
> > @@ -1100,12 +1103,11 @@ EXPORT_SYMBOL_GPL(zs_unmap_object);
> >
> >  u64 zs_get_total_size_bytes(struct zs_pool *pool)
> >  {
> > -       int i;
> > -       u64 npages = 0;
> > -
> > -       for (i = 0; i < ZS_SIZE_CLASSES; i++)
> > -               npages += pool->size_class[i].pages_allocated;
> > +       u64 npages;
> >
> > +       spin_lock(&pool->stat_lock);
> > +       npages = pool->pages_allocated;
> > +       spin_unlock(&pool->stat_lock);
> >         return npages << PAGE_SHIFT;
> >  }
> >  EXPORT_SYMBOL_GPL(zs_get_total_size_bytes);
> > --
> > 2.0.0
> >
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