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Message-ID: <20140814130343.GB966@swordfish> Date: Thu, 14 Aug 2014 22:03:43 +0900 From: Sergey Senozhatsky <sergey.senozhatsky@...il.com> To: Dan Streetman <ddstreet@...e.org> Cc: Sergey Senozhatsky <sergey.senozhatsky@...il.com>, Minchan Kim <minchan@...nel.org>, Linux-MM <linux-mm@...ck.org>, linux-kernel <linux-kernel@...r.kernel.org>, Jerome Marchand <jmarchan@...hat.com>, juno.choi@....com, seungho1.park@....com, Luigi Semenzato <semenzato@...gle.com>, Nitin Gupta <ngupta@...are.org> Subject: Re: [RFC 1/3] zsmalloc: move pages_allocated to zs_pool On (08/13/14 12:11), Dan Streetman wrote: > >> > On Wed, Aug 13, 2014 at 10:14 AM, Sergey Senozhatsky > >> > <sergey.senozhatsky@...il.com> wrote: > >> > > On (08/13/14 09:59), Dan Streetman wrote: > >> > >> On Tue, Aug 5, 2014 at 4:02 AM, Minchan Kim <minchan@...nel.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. > >> > > >> > oh. atomic operations aren't smp safe? is that because other > >> > processors might use a stale value, and barriers must be added? I > >> > guess I don't quite understand the value of atomic then. :-/ > >> > >> pool not only set the value, it also read it and make some decisions > >> based on that value: > >> > >> pages_allocated += X > >> if (pages_allocated >= max_pages_allocated) > >> return 0; > > > > I'm missing where that is? I don't see that in this patch? > > > > > I mean, suppose this happens on two CPUs > > > > max_pages_allocated is 10; current pages_allocated is 8. now you have 2 zs_malloc() > > happenning on two CPUs. each of them will do `pages_allocated += 1'. the problem is > > that both will see 10 at `if (pages_allocated >= max_pages_allocated)', so we will > > fail 2 operations, while we only were supposed to fail one. > > Do you mean this from the 2/3 patch: yeah. sorry for being unclear, I was really sleepy. > @@ -946,6 +947,8 @@ unsigned long zs_malloc(struct zs_pool *pool, size_t size) > set_zspage_mapping(first_page, class->index, ZS_EMPTY); > spin_lock(&pool->stat_lock); > pool->pages_allocated += class->pages_per_zspage; > + if (pool->max_pages_allocated < pool->pages_allocated) > + pool->max_pages_allocated = pool->pages_allocated; > spin_unlock(&pool->stat_lock); > spin_lock(&class->lock); > } > > I see, yeah the max > allocated check before setting is easiest done > with a spinlock. I think pages_allocated could still be done as > atomic, just using atomic_add_return() to grab the current value to > check against, but keeping them the same type and both protected by > the same spinlock I guess simplifies things. Although, if they were > both atomic, then the *only* place that would need a spinlock would be > this check - reading the (atomic) max_pages_allocated wouldn't need a > spinlock, nor would clearing it to 0. makes sense. -ss > >> > >> > >> > >> > > >> > >> > Signed-off-by: Minchan Kim <minchan@...nel.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 > >> > >> > > >> > >> > -- > >> > >> > To unsubscribe, send a message with 'unsubscribe linux-mm' in > >> > >> > the body to majordomo@...ck.org. For more info on Linux MM, > >> > >> > see: http://www.linux-mm.org/ . > >> > >> > Don't email: <a href=mailto:"dont@...ck.org"> email@...ck.org </a> > >> > >> > >> > > >> > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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