Commit f745c6f5 authored by Shakeel Butt's avatar Shakeel Butt Committed by Linus Torvalds
Browse files

fs, mm: account buffer_head to kmemcg 

The buffer_head can consume a significant amount of system memory and is
directly related to the amount of page cache.  In our production
environment we have observed that a lot of machines are spending a
significant amount of memory as buffer_head and can not be left as
system memory overhead.

Charging buffer_head is not as simple as adding __GFP_ACCOUNT to the
allocation.  The buffer_heads can be allocated in a memcg different from
the memcg of the page for which buffer_heads are being allocated.  One
concrete example is memory reclaim.  The reclaim can trigger I/O of
pages of any memcg on the system.  So, the right way to charge
buffer_head is to extract the memcg from the page for which buffer_heads
are being allocated and then use targeted memcg charging API.

[shakeelb@google.com: use __GFP_ACCOUNT for directed memcg charging]
  Link: http://lkml.kernel.org/r/20180702220208.213380-1-shakeelb@google.com
Link: http://lkml.kernel.org/r/20180627191250.209150-3-shakeelb@google.com


Signed-off-by: default avatarShakeel Butt <shakeelb@google.com>
Acked-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Amir Goldstein <amir73il@gmail.com>
Cc: Greg Thelen <gthelen@google.com>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent d46eb14b

fs/buffer.c

+10 −2
Original line number Diff line number Diff line
@@ -45,6 +45,7 @@ 
#include <linux/mpage.h>

#include <linux/bit_spinlock.h>

#include <linux/pagevec.h>

#include <linux/sched/mm.h>

#include <trace/events/block.h>



static int fsync_buffers_list(spinlock_t *lock, struct list_head *list);
@@ -813,12 +814,16 @@ struct buffer_head *alloc_page_buffers(struct page *page, unsigned long size, 
		bool retry)

{

	struct buffer_head *bh, *head;

	gfp_t gfp = GFP_NOFS;

	gfp_t gfp = GFP_NOFS | __GFP_ACCOUNT;

	long offset;

	struct mem_cgroup *memcg;



	if (retry)

		gfp |= __GFP_NOFAIL;



	memcg = get_mem_cgroup_from_page(page);

	memalloc_use_memcg(memcg);



	head = NULL;

	offset = PAGE_SIZE;

	while ((offset -= size) >= 0) {
@@ -835,6 +840,9 @@ struct buffer_head *alloc_page_buffers(struct page *page, unsigned long size, 
		/* Link the buffer to its page */

		set_bh_page(bh, page, offset);

	}

out:

	memalloc_unuse_memcg();

	mem_cgroup_put(memcg);

	return head;

/*

 * In case anything failed, we just free everything we got.
@@ -848,7 +856,7 @@ no_grow: 
		} while (head);

	}



	return NULL;

	goto out;

}

EXPORT_SYMBOL_GPL(alloc_page_buffers);

include/linux/memcontrol.h

+7 −0
Original line number Diff line number Diff line
@@ -375,6 +375,8 @@ struct mem_cgroup *mem_cgroup_from_task(struct task_struct *p); 


struct mem_cgroup *get_mem_cgroup_from_mm(struct mm_struct *mm);



struct mem_cgroup *get_mem_cgroup_from_page(struct page *page);



static inline

struct mem_cgroup *mem_cgroup_from_css(struct cgroup_subsys_state *css){

	return css ? container_of(css, struct mem_cgroup, css) : NULL;
@@ -863,6 +865,11 @@ static inline struct mem_cgroup *get_mem_cgroup_from_mm(struct mm_struct *mm) 
	return NULL;

}



static inline struct mem_cgroup *get_mem_cgroup_from_page(struct page *page)

{

	return NULL;

}



static inline void mem_cgroup_put(struct mem_cgroup *memcg)

{

}

mm/memcontrol.c

+22 −0
Original line number Diff line number Diff line
@@ -713,6 +713,28 @@ struct mem_cgroup *get_mem_cgroup_from_mm(struct mm_struct *mm) 
}

EXPORT_SYMBOL(get_mem_cgroup_from_mm);



/**

 * get_mem_cgroup_from_page: Obtain a reference on given page's memcg.

 * @page: page from which memcg should be extracted.

 *

 * Obtain a reference on page->memcg and returns it if successful. Otherwise

 * root_mem_cgroup is returned.

 */

struct mem_cgroup *get_mem_cgroup_from_page(struct page *page)

{

	struct mem_cgroup *memcg = page->mem_cgroup;



	if (mem_cgroup_disabled())

		return NULL;



	rcu_read_lock();

	if (!memcg || !css_tryget_online(&memcg->css))

		memcg = root_mem_cgroup;

	rcu_read_unlock();

	return memcg;

}

EXPORT_SYMBOL(get_mem_cgroup_from_page);



/**

 * If current->active_memcg is non-NULL, do not fallback to current->mm->memcg.

 */

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