linux-kernel - Re: cgroup: rmdir() does not complete

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Date:	Fri, 10 Sep 2010 13:05:39 +0900
From:	Daisuke Nishimura <nishimura@....nes.nec.co.jp>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Mark Hills <mark@...o.org.uk>,
	Peter Zijlstra <peterz@...radead.org>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>
Subject: Re: cgroup: rmdir() does not complete

On Fri, 10 Sep 2010 11:16:46 +0900
KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:

> On Fri, 10 Sep 2010 00:04:31 +0100 (BST)
> Mark Hills <mark@...o.org.uk> wrote:
> > The report on the spinning process (23586) is dominated by calls from 
> > mem_cgroup_force_empty.
> > 
> > It seems to show lru_add_drain_all and drain_all_stock_sync are causing 
> > the load (I assume drain_all_stock_sync has been optimised out). But I 
> > don't think this is as important as what causes the spin.
> > 
> 
> I noticed you use FUSE and it seems there is a problem in FUSE v.s. memcg.
> I wrote a patch (onto 2.6.36 but can be applied..)
> 
Nice catch!

> Could you try this ? I'm sorry I don't use FUSE system and can't test
> right now.
> 
Sorry, I can't either.

> ==
> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> 
> memory cgroup catches all pages which is added to radix-tree and
> assumes the pages will be added to LRU, somewhere.
> But there are pages which not on LRU but on radix-tree. Then,
> force_empty cannot find them and cannot finish ->pre_destroy(), rmdir
> operations.
> 
> This patch adds __GFP_NOMEMCGROUP and avoids unnecessary, out-of-control
> pages are registered to memory cgroup. 
> 
> Note: This gfp flag can be used for shmem handling, which now uses
>       complicated heuristics.
> 
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> ---
>  fs/fuse/dev.c       |   11 ++++++++++-
>  include/linux/gfp.h |    7 +++++++
>  mm/memcontrol.c     |    2 +-
>  3 files changed, 18 insertions(+), 2 deletions(-)
> 
> Index: linux-2.6.36-rc3/fs/fuse/dev.c
> ===================================================================
> --- linux-2.6.36-rc3.orig/fs/fuse/dev.c
> +++ linux-2.6.36-rc3/fs/fuse/dev.c
> @@ -19,6 +19,7 @@
>  #include <linux/pipe_fs_i.h>
>  #include <linux/swap.h>
>  #include <linux/splice.h>
> +#include <linux/memcontrol.h>
>  
>  MODULE_ALIAS_MISCDEV(FUSE_MINOR);
>  MODULE_ALIAS("devname:fuse");
> @@ -683,6 +684,7 @@ static int fuse_try_move_page(struct fus
>  	struct pipe_buffer *buf = cs->pipebufs;
>  	struct address_space *mapping;
>  	pgoff_t index;
> +	gfp_t mask = GFP_KERNEL;
>  
>  	unlock_request(cs->fc, cs->req);
>  	fuse_copy_finish(cs);
> @@ -732,7 +734,14 @@ static int fuse_try_move_page(struct fus
>  	remove_from_page_cache(oldpage);
>  	page_cache_release(oldpage);
>  
> -	err = add_to_page_cache_locked(newpage, mapping, index, GFP_KERNEL);
> +	/*
> +	 * not-on-LRU pages are out of control. So, add to root cgroup.
> + 	 * See mm/memcontrol.c for details.
> +	 */
> +	if (buf->flags & PIPE_BUF_FLAG_LRU)
> +		mask |= __GFP_NOMEMCGROUP;
> +
> +	err = add_to_page_cache_locked(newpage, mapping, index, mask);
>  	if (err) {
>  		printk(KERN_WARNING "fuse_try_move_page: failed to add page");
>  		goto out_fallback_unlock;
> Index: linux-2.6.36-rc3/include/linux/gfp.h
> ===================================================================
> --- linux-2.6.36-rc3.orig/include/linux/gfp.h
> +++ linux-2.6.36-rc3/include/linux/gfp.h
> @@ -60,6 +60,13 @@ struct vm_area_struct;
>  #define __GFP_NOTRACK	((__force gfp_t)0)
>  #endif
>  
> +#ifdef CONFIG_CGROUP_MEM_RES_CTLR
> +#define __GFP_NOMEMCGROUP	((__force gfp_t)0x400000u)
> +	/* Don't track by memory cgroup */
> +#else
> +#define __GFP_NOMEMCGROUP	((__force gfp_t)0)
> +#endif
> +
>  /*
>   * This may seem redundant, but it's a way of annotating false positives vs.
>   * allocations that simply cannot be supported (e.g. page tables).
> Index: linux-2.6.36-rc3/mm/memcontrol.c
> ===================================================================
> --- linux-2.6.36-rc3.orig/mm/memcontrol.c
> +++ linux-2.6.36-rc3/mm/memcontrol.c
> @@ -2114,7 +2114,7 @@ int mem_cgroup_cache_charge(struct page 
>  
>  	if (mem_cgroup_disabled())
>  		return 0;
> -	if (PageCompound(page))
> +	if (PageCompound(page) || (gfp_mask & __GFP_NOMEMCGROUP))
>  		return 0;
>  	/*
>  	 * Corner case handling. This is called from add_to_page_cache()
> 
The comments above says "not-on-LRU pages are out of control. So, add to root cgroup.".
But this change means that we don't charge these pages at all.

Should it be:

	if (gfp_mask & __GFP_NOMEMCGROUP))
		mm = &init_mm;

?
Or, change the comment ?


Thanks,
Daisuke Nishimura.
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