linux-kernel - Re: [PATCH v2] zbud: allow up to PAGE

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Date:	Fri, 25 Sep 2015 17:05:25 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Seth Jennings <sjennings@...iantweb.net>,
	Vitaly Wool <vitalywool@...il.com>,
	Dan Streetman <ddstreet@...e.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Linux-MM <linux-mm@...ck.org>
Subject: Re: [PATCH v2] zbud: allow up to PAGE_SIZE allocations

On (09/25/15 11:13), Minchan Kim wrote:
> > Ok, I can see that having the allocator backends for zpool 
> > have the same set of constraints is nice.
> 
> Sorry for delay. I'm on vacation until next week.
> It seems Seth was missed in previous discusstion which was not the end.
> 
> I already said questions, opinion and concerns but anything is not clear
> until now. Only clear thing I could hear is just "compaction stats are
> better" which is not enough for me. Sorry.

Agree.

There weren't lots of answers, really.

Vitaly,

Have you seen those symptoms before? How did you come up to a conclusion
that zram->zbud will do the trick?

If those symptoms are some sort of a recent addition, then does it help
when you disable zsmalloc compaction?

---

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index f59e8eb..b6c6a19 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -1944,8 +1944,8 @@ struct zs_pool *zs_create_pool(const char *name, gfp_t flags)
         * Not critical, we still can use the pool
         * and user can trigger compaction manually.
         */
-       if (zs_register_shrinker(pool) == 0)
-               pool->shrinker_enabled = true;
+/*     if (zs_register_shrinker(pool) == 0)
+               pool->shrinker_enabled = true;*/
        return pool;
 
 err:

---


p.s. I'll be on vacation next week, so most likely will be quite slow
to answer.

	-ss

> 
> 1) https://lkml.org/lkml/2015/9/15/33
> 2) https://lkml.org/lkml/2015/9/21/2
> 
> Vitally, Please say what's the root cause of your problem and if it
> is external fragmentation, what's the problem of my approach?
> 
> 1) make non-LRU page migrate
> 2) provide zsmalloc's migratpage
> 
> We should provide it for CMA as well as external fragmentation.
> I think we could solve your issue with above approach and
> it fundamentally makes zsmalloc/zbud happy in future.
> 
> Also, please keep it in mind that zram has been in linux kernel for
> memory efficiency for a long time and later zswap/zbud was born
> for *determinism* at the cost of memory efficiency.
> 
> Thanks.
> 
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