`2014-11-21 18:32 GMT+08:00 Minchan Kim <minchan@kernel.org>:> On Fri, Nov 21, 2014 at 06:48:49AM +0000, Minchan Kim wrote:>> On Fri, Nov 21, 2014 at 01:33:26PM +0800, Ganesh Mahendran wrote:>> > Hello>> >>> > 2014-11-21 11:54 GMT+08:00 Minchan Kim <minchan@kernel.org>:>> > > On Thu, Nov 20, 2014 at 09:21:56PM +0800, Mahendran Ganesh wrote:>> > >> ZS_SIZE_CLASSES is calc by:>> > >>   ((ZS_MAX_ALLOC_SIZE - ZS_MIN_ALLOC_SIZE) / ZS_SIZE_CLASS_DELTA + 1)>> > >>>> > >> So when i is in [0, ZS_SIZE_CLASSES - 1), the size:>> > >>   size = ZS_MIN_ALLOC_SIZE + i * ZS_SIZE_CLASS_DELTA>> > >> will not be greater than ZS_MAX_ALLOC_SIZE>> > >>>> > >> This patch removes the unnecessary check.>> > >>> > > It depends on ZS_MIN_ALLOC_SIZE.>> > > For example, we would change min to 8 but MAX is still 4096.>> > > ZS_SIZE_CLASSES is (4096 - 8) / 16 + 1 = 256 so 8 + 255 * 16 = 4088,>> > > which exceeds the max.>> > Here, 4088 is less than MAX(4096).>> >>> > ZS_SIZE_CLASSES = (MAX - MIN) / Delta + 1>> > So, I think the value of>> >     MIN + (ZS_SIZE_CLASSES - 1) * Delta =>> >     MIN + ((MAX - MIN) / Delta) * Delta =>> >     MAX>> > will not exceed the MAX>>>> You're right. It was complext math for me.>> I should go back to elementary school.>>>> Thanks!>>>> Acked-by: Minchan Kim <minchan@kernel.org>>> I catch a nasty cold but above my poor math makes me think more.> ZS_SIZE_CLASSES is broken. In above my example, current code cannot> allocate 4096 size class so we should correct ZS_SIZE_CLASSES> at first.>> zs_size_classes = zs_max - zs_min / delta + 1;> if ((zs_max - zs_min) % delta)>         zs_size_classes += 1;>> Then, we need to code piece you removed.> As well, we need to fix below.>> - area->vm_buf = (char *)__get_free_page(GFP_KERNEL);> + area->vm_buf = kmalloc(ZS_MAX_ALLOC_SIZE);>> Hope I am sane in this time :(how about something like this?In zsmalloc, if ZS_MIN_ALLOC_SIZE is less than ZS_SIZE_CLASS_DELTA.Max obj size (ZS_MIN_ALLOC_SIZE + ZS_SIZE_CLASSES * ZS_SIZE_CLASS_DELTA)will be less than ZS_MAX_ALLOC_SIZE(page size).And in zs_malloc(), we thought we can put an obj(len == PAGE_SIZE)into zsmalloc. But actually we can not. This will make user confused.This patch takes Minchan Kim's suggestion.    https://lkml.org/lkml/2014/11/21/172When (ZS_MAX_ALLOC_SIZE - ZS_MIN_ALLOC_SIZE) % ZS_SIZE_CLASS_DELTA) != 0,we add increase sz_size_class by 1 to make the size of max obj equal toZS_MAX_ALLOC_SIZE(PAGE_SIZE).Signed-off-by: Mahendran Ganesh <opensource.ganesh@gmail.com>--- mm/zsmalloc.c |   22 +++++++++++++++++----- 1 file changed, 17 insertions(+), 5 deletions(-)diff --git a/mm/zsmalloc.c b/mm/zsmalloc.cindex 810eda1..bcea72d 100644--- a/mm/zsmalloc.c+++ b/mm/zsmalloc.c@@ -155,8 +155,6 @@  *  (reason above)  */ #define ZS_SIZE_CLASS_DELTA	(PAGE_SIZE >> 8)-#define ZS_SIZE_CLASSES		((ZS_MAX_ALLOC_SIZE - ZS_MIN_ALLOC_SIZE) / \-					ZS_SIZE_CLASS_DELTA + 1)  /*  * We do not maintain any list for completely empty or full pages@@ -214,7 +212,8 @@ struct link_free { };  struct zs_pool {-	struct size_class *size_class[ZS_SIZE_CLASSES];+	struct size_class **size_class;+	int nr_size_classes;  	gfp_t flags;	/* allocation flags used when growing pool */ 	atomic_long_t pages_allocated;@@ -956,17 +955,28 @@ struct zs_pool *zs_create_pool(gfp_t flags) { 	int i, ovhd_size; 	struct zs_pool *pool;+	int nr;  	ovhd_size = roundup(sizeof(*pool), PAGE_SIZE); 	pool = kzalloc(ovhd_size, GFP_KERNEL); 	if (!pool) 		return NULL; +	nr = (ZS_MAX_ALLOC_SIZE - ZS_MIN_ALLOC_SIZE) / ZS_SIZE_CLASS_DELTA + 1;+	if ((ZS_MAX_ALLOC_SIZE - ZS_MIN_ALLOC_SIZE) % ZS_SIZE_CLASS_DELTA)+		nr += 1;++	pool->size_class = kcalloc(nr, sizeof(struct size_class *),+			GFP_KERNEL);+	if (!pool->size_class)+		goto err;+	pool->nr_size_classes = nr;+ 	/* 	 * Iterate reversly, because, size of size_class that we want to use 	 * for merging should be larger or equal to current size. 	 */-	for (i = ZS_SIZE_CLASSES - 1; i >= 0; i--) {+	for (i = pool->nr_size_classes - 1; i >= 0; i--) { 		int size; 		int pages_per_zspage; 		struct size_class *class;@@ -1020,7 +1030,7 @@ void zs_destroy_pool(struct zs_pool *pool) { 	int i; -	for (i = 0; i < ZS_SIZE_CLASSES; i++) {+	for (i = 0; i < pool->nr_size_classes; i++) { 		int fg; 		struct size_class *class = pool->size_class[i]; @@ -1038,6 +1048,8 @@ void zs_destroy_pool(struct zs_pool *pool) 		} 		kfree(class); 	}++	kfree(pool->size_class); 	kfree(pool); } EXPORT_SYMBOL_GPL(zs_destroy_pool);-- 1.7.9.5`