Commit b6038942 authored by Shakeel Butt's avatar Shakeel Butt Committed by Linus Torvalds
Browse files

mm: memcg: add swapcache stat for memcg v2 

This patch adds swapcache stat for the cgroup v2.  The swapcache
represents the memory that is accounted against both the memory and the
swap limit of the cgroup.  The main motivation behind exposing the
swapcache stat is for enabling users to gracefully migrate from cgroup
v1's memsw counter to cgroup v2's memory and swap counters.

Cgroup v1's memsw limit allows users to limit the memory+swap usage of a
workload but without control on the exact proportion of memory and swap.
Cgroup v2 provides separate limits for memory and swap which enables more
control on the exact usage of memory and swap individually for the
workload.

With some little subtleties, the v1's memsw limit can be switched with the
sum of the v2's memory and swap limits.  However the alternative for memsw
usage is not yet available in cgroup v2.  Exposing per-cgroup swapcache
stat enables that alternative.  Adding the memory usage and swap usage and
subtracting the swapcache will approximate the memsw usage.  This will
help in the transparent migration of the workloads depending on memsw
usage and limit to v2' memory and swap counters.

The reasons these applications are still interested in this approximate
memsw usage are: (1) these applications are not really interested in two
separate memory and swap usage metrics.  A single usage metric is more
simple to use and reason about for them.

(2) The memsw usage metric hides the underlying system's swap setup from
the applications.  Applications with multiple instances running in a
datacenter with heterogeneous systems (some have swap and some don't) will
keep seeing a consistent view of their usage.

[akpm@linux-foundation.org: fix CONFIG_SWAP=n build]

Link: https://lkml.kernel.org/r/20210108155813.2914586-3-shakeelb@google.com


Signed-off-by: default avatarShakeel Butt <shakeelb@google.com>
Acked-by: default avatarMichal Hocko <mhocko@suse.com>
Reviewed-by: default avatarRoman Gushchin <guro@fb.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Yang Shi <shy828301@gmail.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent f9b1038e

Documentation/admin-guide/cgroup-v2.rst

+4 −0
Original line number Diff line number Diff line
@@ -1299,6 +1299,10 @@ PAGE_SIZE multiple when read back. 
		Amount of cached filesystem data that was modified and

		is currently being written back to disk



	  swapcached

		Amount of swap cached in memory. The swapcache is accounted

		against both memory and swap usage.



	  anon_thp

		Amount of memory used in anonymous mappings backed by

		transparent hugepages

drivers/base/node.c

+6 −0
Original line number Diff line number Diff line
@@ -372,14 +372,19 @@ static ssize_t node_read_meminfo(struct device *dev, 
	struct pglist_data *pgdat = NODE_DATA(nid);

	struct sysinfo i;

	unsigned long sreclaimable, sunreclaimable;

	unsigned long swapcached = 0;



	si_meminfo_node(&i, nid);

	sreclaimable = node_page_state_pages(pgdat, NR_SLAB_RECLAIMABLE_B);

	sunreclaimable = node_page_state_pages(pgdat, NR_SLAB_UNRECLAIMABLE_B);

#ifdef CONFIG_SWAP

	swapcached = node_page_state_pages(pgdat, NR_SWAPCACHE);

#endif

	len = sysfs_emit_at(buf, len,

			    "Node %d MemTotal:       %8lu kB\n"

			    "Node %d MemFree:        %8lu kB\n"

			    "Node %d MemUsed:        %8lu kB\n"

			    "Node %d SwapCached:     %8lu kB\n"

			    "Node %d Active:         %8lu kB\n"

			    "Node %d Inactive:       %8lu kB\n"

			    "Node %d Active(anon):   %8lu kB\n"
@@ -391,6 +396,7 @@ static ssize_t node_read_meminfo(struct device *dev, 
			    nid, K(i.totalram),

			    nid, K(i.freeram),

			    nid, K(i.totalram - i.freeram),

			    nid, K(swapcached),

			    nid, K(node_page_state(pgdat, NR_ACTIVE_ANON) +

				   node_page_state(pgdat, NR_ACTIVE_FILE)),

			    nid, K(node_page_state(pgdat, NR_INACTIVE_ANON) +

include/linux/mmzone.h

+3 −0
Original line number Diff line number Diff line
@@ -206,6 +206,9 @@ enum node_stat_item { 
	NR_KERNEL_SCS_KB,	/* measured in KiB */

#endif

	NR_PAGETABLE,		/* used for pagetables */

#ifdef CONFIG_SWAP

	NR_SWAPCACHE,

#endif

	NR_VM_NODE_STAT_ITEMS

};

include/linux/swap.h

+5 −1
Original line number Diff line number Diff line
@@ -408,7 +408,11 @@ extern struct address_space *swapper_spaces[]; 
#define swap_address_space(entry)			    \

	(&swapper_spaces[swp_type(entry)][swp_offset(entry) \

		>> SWAP_ADDRESS_SPACE_SHIFT])

extern unsigned long total_swapcache_pages(void);

static inline unsigned long total_swapcache_pages(void)

{

	return global_node_page_state(NR_SWAPCACHE);

}



extern void show_swap_cache_info(void);

extern int add_to_swap(struct page *page);

extern void *get_shadow_from_swap_cache(swp_entry_t entry);

mm/memcontrol.c

+3 −0
Original line number Diff line number Diff line
@@ -1521,6 +1521,9 @@ static const struct memory_stat memory_stats[] = { 
	{ "file_mapped",		NR_FILE_MAPPED			},

	{ "file_dirty",			NR_FILE_DIRTY			},

	{ "file_writeback",		NR_WRITEBACK			},

#ifdef CONFIG_SWAP

	{ "swapcached",			NR_SWAPCACHE			},

#endif

#ifdef CONFIG_TRANSPARENT_HUGEPAGE

	{ "anon_thp",			NR_ANON_THPS			},

	{ "file_thp",			NR_FILE_THPS			},