Re: [PATCH] mm: memcontrol: MEMCG no longer works with SLOB
From: Vladimir Davydov <hidden>
Date: 2015-12-10 11:25:05
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On Wed, Dec 09, 2015 at 03:01:07PM -0500, Johannes Weiner wrote:
On Wed, Dec 09, 2015 at 05:32:39PM +0100, Arnd Bergmann wrote:quoted
The change to move the kmem accounting into the normal memcg code means we can no longer use memcg with slob, which lacks the memcg_params member in its struct kmem_cache: ../mm/slab.h: In function 'is_root_cache': ../mm/slab.h:187:10: error: 'struct kmem_cache' has no member named 'memcg_params'
Argh, I completely forgot about this SLOB thing :-(
quoted hunk ↗ jump to hunk
quoted
This enforces the new dependency in Kconfig. Alternatively, we could change the slob code to allow using MEMCG.I'm curious, was this a random config or do you actually use CONFIG_SLOB && CONFIG_MEMCG? Excluding CONFIG_MEMCG completely for slob seems harsh, but I would prefer not littering the source with #if defined(CONFIG_MEMCG) && (defined(CONFIG_SLAB) || defined(CONFIG_SLUB)) or #if defined(CONFIG_MEMCG) && !defined(CONFIG_SLOB) for such a special case. The #ifdefs are already out of hand in there. Vladimir, what would you think of simply doing this?diff --git a/mm/slab.h b/mm/slab.h index 5adec08..0b3ec4b 100644 --- a/mm/slab.h +++ b/mm/slab.h@@ -25,6 +25,9 @@ struct kmem_cache { int refcount; /* Use counter */ void (*ctor)(void *); /* Called on object slot creation */ struct list_head list; /* List of all slab caches on the system */ +#ifdef CONFIG_MEMCG + struct memcg_cache_params memcg_params; +#endif }; #endif /* CONFIG_SLOB */
I don't like it. This would result in allocation of per memcg arrays for each list_lru/kmem_cache, which would never be used. This looks extremely ugly. I'd prefer to make CONFIG_MEMCG depend on SL[AU]B, but I'm afraid such a change will be frowned upon - who knows who uses MEMCG & SLOB? I guess SLOB could be made memcg-aware, but I don't think it's worth the trouble, although I can take a look in this direction - from a quick glance at SLOB it shouldn't be difficult. If we decide to go this way, I think we could use this patch as a temporary fix, which would be reverted eventually. Otherwise, no matter how tempting the idea to put all memcg stuff under CONFIG_MEMCG is, I think it won't fly, so for now we should use ifdefs. To avoid complex checks, we could define a macro in memcontrol.h, say MEMCG_KMEM_ENABLED, and use it throughout the code. And I think we should wrap list_lru stuff in it either :-/ Thanks, Vladimir