On Thu, Aug 09 2012, Glauber Costa wrote:
> This patch introduces infrastructure for tracking kernel memory pages to
> a given memcg. This will happen whenever the caller includes the flag
> __GFP_KMEMCG flag, and the task belong to a memcg other than the root.
>
> In memcontrol.h those functions are wrapped in inline accessors. The
> idea is to later on, patch those with static branches, so we don't incur
> any overhead when no mem cgroups with limited kmem are being used.
>
> [ v2: improved comments and standardized function names ]
>
> Signed-off-by: Glauber Costa <glom...@parallels.com>
> CC: Christoph Lameter <c...@linux.com>
> CC: Pekka Enberg <penb...@cs.helsinki.fi>
> CC: Michal Hocko <mho...@suse.cz>
> CC: Kamezawa Hiroyuki <kamezawa.hir...@jp.fujitsu.com>
> CC: Johannes Weiner <han...@cmpxchg.org>
> ---
> include/linux/memcontrol.h | 79 +++++++++++++++++++
> mm/memcontrol.c | 185
> +++++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 264 insertions(+)
>
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 8d9489f..75b247e 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -21,6 +21,7 @@
> #define _LINUX_MEMCONTROL_H
> #include <linux/cgroup.h>
> #include <linux/vm_event_item.h>
> +#include <linux/hardirq.h>
>
> struct mem_cgroup;
> struct page_cgroup;
> @@ -399,6 +400,11 @@ struct sock;
> #ifdef CONFIG_MEMCG_KMEM
> void sock_update_memcg(struct sock *sk);
> void sock_release_memcg(struct sock *sk);
> +
> +#define memcg_kmem_on 1
> +bool __memcg_kmem_new_page(gfp_t gfp, void *handle, int order);
> +void __memcg_kmem_commit_page(struct page *page, void *handle, int order);
> +void __memcg_kmem_free_page(struct page *page, int order);
> #else
> static inline void sock_update_memcg(struct sock *sk)
> {
> @@ -406,6 +412,79 @@ static inline void sock_update_memcg(struct sock *sk)
> static inline void sock_release_memcg(struct sock *sk)
> {
> }
> +
> +#define memcg_kmem_on 0
> +static inline bool
> +__memcg_kmem_new_page(gfp_t gfp, void *handle, int order)
> +{
> + return false;
> +}
> +
> +static inline void __memcg_kmem_free_page(struct page *page, int order)
> +{
> +}
> +
> +static inline void
> +__memcg_kmem_commit_page(struct page *page, struct mem_cgroup *handle, int
> order)
> +{
> +}
> #endif /* CONFIG_MEMCG_KMEM */
> +
> +/**
> + * memcg_kmem_new_page: verify if a new kmem allocation is allowed.
> + * @gfp: the gfp allocation flags.
> + * @handle: a pointer to the memcg this was charged against.
> + * @order: allocation order.
> + *
> + * returns true if the memcg where the current task belongs can hold this
> + * allocation.
> + *
> + * We return true automatically if this allocation is not to be accounted to
> + * any memcg.
> + */
> +static __always_inline bool
> +memcg_kmem_new_page(gfp_t gfp, void *handle, int order)
> +{
> + if (!memcg_kmem_on)
> + return true;
> + if (!(gfp & __GFP_KMEMCG) || (gfp & __GFP_NOFAIL))
> + return true;
> + if (in_interrupt() || (!current->mm) || (current->flags & PF_KTHREAD))
> + return true;
> + return __memcg_kmem_new_page(gfp, handle, order);
> +}
> +
> +/**
> + * memcg_kmem_free_page: uncharge pages from memcg
> + * @page: pointer to struct page being freed
> + * @order: allocation order.
> + *
> + * there is no need to specify memcg here, since it is embedded in
> page_cgroup
> + */
> +static __always_inline void
> +memcg_kmem_free_page(struct page *page, int order)
> +{
> + if (memcg_kmem_on)
> + __memcg_kmem_free_page(page, order);
> +}
> +
> +/**
> + * memcg_kmem_commit_page: embeds correct memcg in a page
> + * @handle: a pointer to the memcg this was charged against.
> + * @page: pointer to struct page recently allocated
> + * @handle: the memcg structure we charged against
> + * @order: allocation order.
> + *
> + * Needs to be called after memcg_kmem_new_page, regardless of success or
> + * failure of the allocation. if @page is NULL, this function will revert the
> + * charges. Otherwise, it will commit the memcg given by @handle to the
> + * corresponding page_cgroup.
> + */
> +static __always_inline void
> +memcg_kmem_commit_page(struct page *page, struct mem_cgroup *handle, int
> order)
> +{
> + if (memcg_kmem_on)
> + __memcg_kmem_commit_page(page, handle, order);
> +}
> #endif /* _LINUX_MEMCONTROL_H */
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 54e93de..e9824c1 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -10,6 +10,10 @@
> * Copyright (C) 2009 Nokia Corporation
> * Author: Kirill A. Shutemov
> *
> + * Kernel Memory Controller
> + * Copyright (C) 2012 Parallels Inc. and Google Inc.
> + * Authors: Glauber Costa and Suleiman Souhlal
> + *
> * This program is free software; you can redistribute it and/or modify
> * it under the terms of the GNU General Public License as published by
> * the Free Software Foundation; either version 2 of the License, or
> @@ -434,6 +438,9 @@ struct mem_cgroup *mem_cgroup_from_css(struct
> cgroup_subsys_state *s)
> #include <net/ip.h>
>
> static bool mem_cgroup_is_root(struct mem_cgroup *memcg);
> +static int memcg_charge_kmem(struct mem_cgroup *memcg, gfp_t gfp, s64 delta);
> +static void memcg_uncharge_kmem(struct mem_cgroup *memcg, s64 delta);
> +
> void sock_update_memcg(struct sock *sk)
> {
> if (mem_cgroup_sockets_enabled) {
> @@ -488,6 +495,118 @@ struct cg_proto *tcp_proto_cgroup(struct mem_cgroup
> *memcg)
> }
> EXPORT_SYMBOL(tcp_proto_cgroup);
> #endif /* CONFIG_INET */
> +
> +static inline bool memcg_kmem_enabled(struct mem_cgroup *memcg)
> +{
> + return !mem_cgroup_disabled() && !mem_cgroup_is_root(memcg) &&
> + memcg->kmem_accounted;
> +}
> +
> +/*
> + * We need to verify if the allocation against current->mm->owner's memcg is
> + * possible for the given order. But the page is not allocated yet, so we'll
> + * need a further commit step to do the final arrangements.
> + *
> + * It is possible for the task to switch cgroups in this mean time, so at
> + * commit time, we can't rely on task conversion any longer. We'll then use
> + * the handle argument to return to the caller which cgroup we should commit
> + * against
> + *
> + * Returning true means the allocation is possible.
> + */
> +bool __memcg_kmem_new_page(gfp_t gfp, void *_handle, int order)
> +{
> + struct mem_cgroup *memcg;
> + struct mem_cgroup **handle = (struct mem_cgroup **)_handle;
> + bool ret = true;
> + size_t size;
> + struct task_struct *p;
> +
> + *handle = NULL;
> + rcu_read_lock();
> + p = rcu_dereference(current->mm->owner);
> + memcg = mem_cgroup_from_task(p);
> + if (!memcg_kmem_enabled(memcg))
> + goto out;
> +
> + mem_cgroup_get(memcg);
> +
> + size = PAGE_SIZE << order;
> + ret = memcg_charge_kmem(memcg, gfp, size) == 0;
> + if (!ret) {
> + mem_cgroup_put(memcg);
> + goto out;
> + }
> +
> + *handle = memcg;
> +out:
> + rcu_read_unlock();
> + return ret;
> +}
> +EXPORT_SYMBOL(__memcg_kmem_new_page);
> +
> +void __memcg_kmem_commit_page(struct page *page, void *handle, int order)
> +{
> + struct page_cgroup *pc;
> + struct mem_cgroup *memcg = handle;
> +
> + if (!memcg)
> + return;
> +
> + WARN_ON(mem_cgroup_is_root(memcg));
> + /* The page allocation must have failed. Revert */
> + if (!page) {
> + size_t size = PAGE_SIZE << order;
> +
> + memcg_uncharge_kmem(memcg, size);
> + mem_cgroup_put(memcg);
> + return;
> +
> + pc = lookup_page_cgroup(page);
> + lock_page_cgroup(pc);
> + pc->mem_cgroup = memcg;
> + SetPageCgroupUsed(pc);
> + unlock_page_cgroup(pc);
I have no problem with the code here. But, out of curiosity, why do we
need to lock the pc here and below in __memcg_kmem_free_page()?
For the allocating side, I don't think that migration or reclaim will be
manipulating this page. But is there something else that we need the
locking for?
For the freeing side, it seems that anyone calling
__memcg_kmem_free_page() is going to be freeing a previously accounted
page.
I imagine that if we did not need the locking we would still need some
memory barriers to make sure that modifications to the PG_lru are
serialized wrt. to kmem modifying PageCgroupUsed here.
Perhaps we're just trying to take a conservative initial implementation
which is consistent with user visible pages.
> +}
> +
> +void __memcg_kmem_free_page(struct page *page, int order)
> +{
> + struct mem_cgroup *memcg;
> + size_t size;
> + struct page_cgroup *pc;
> +
> + if (mem_cgroup_disabled())
> + return;
> +
> + pc = lookup_page_cgroup(page);
> + lock_page_cgroup(pc);
> + memcg = pc->mem_cgroup;
> + pc->mem_cgroup = NULL;
> + if (!PageCgroupUsed(pc)) {
When do we expect to find PageCgroupUsed() unset in this routine? Is
this just to handle the race of someone enabling kmem accounting after
allocating a page and then later freeing that page?
> + unlock_page_cgroup(pc);
> + return;
> + }
> + ClearPageCgroupUsed(pc);
> + unlock_page_cgroup(pc);
> +
> + /*
> + * Checking if kmem accounted is enabled won't work for uncharge, since
> + * it is possible that the user enabled kmem tracking, allocated, and
> + * then disabled it again.
> + *
> + * We trust if there is a memcg associated with the page, it is a valid
> + * allocation
> + */
> + if (!memcg)
> + return;
> +
> + WARN_ON(mem_cgroup_is_root(memcg));
> + size = (1 << order) << PAGE_SHIFT;
> + memcg_uncharge_kmem(memcg, size);
> + mem_cgroup_put(memcg);
> +}
> +EXPORT_SYMBOL(__memcg_kmem_free_page);
> #endif /* CONFIG_MEMCG_KMEM */
>
> #if defined(CONFIG_INET) && defined(CONFIG_MEMCG_KMEM)
> @@ -5759,3 +5878,69 @@ static int __init enable_swap_account(char *s)
> __setup("swapaccount=", enable_swap_account);
>
> #endif
> +
> +#ifdef CONFIG_MEMCG_KMEM
> +int memcg_charge_kmem(struct mem_cgroup *memcg, gfp_t gfp, s64 delta)
> +{
> + struct res_counter *fail_res;
> + struct mem_cgroup *_memcg;
> + int ret;
> + bool may_oom;
> + bool nofail = false;
> +
> + may_oom = (gfp & __GFP_WAIT) && (gfp & __GFP_FS) &&
> + !(gfp & __GFP_NORETRY);
> +
> + ret = 0;
> +
> + if (!memcg)
> + return ret;
> +
> + _memcg = memcg;
> + ret = __mem_cgroup_try_charge(NULL, gfp, delta / PAGE_SIZE,
> + &_memcg, may_oom);
> +
> + if (ret == -EINTR) {
> + nofail = true;
> + /*
> + * __mem_cgroup_try_charge() chosed to bypass to root due to
> + * OOM kill or fatal signal. Since our only options are to
> + * either fail the allocation or charge it to this cgroup, do
> + * it as a temporary condition. But we can't fail. From a
> + * kmem/slab perspective, the cache has already been selected,
> + * by mem_cgroup_get_kmem_cache(), so it is too late to change
> + * our minds
> + */
> + res_counter_charge_nofail(&memcg->res, delta, &fail_res);
> + if (do_swap_account)
> + res_counter_charge_nofail(&memcg->memsw, delta,
> + &fail_res);
> + ret = 0;
> + } else if (ret == -ENOMEM)
> + return ret;
> +
> + if (nofail)
> + res_counter_charge_nofail(&memcg->kmem, delta, &fail_res);
> + else
> + ret = res_counter_charge(&memcg->kmem, delta, &fail_res);
> +
> + if (ret) {
> + res_counter_uncharge(&memcg->res, delta);
> + if (do_swap_account)
> + res_counter_uncharge(&memcg->memsw, delta);
> + }
> +
> + return ret;
> +}
> +
> +void memcg_uncharge_kmem(struct mem_cgroup *memcg, s64 delta)
> +{
> + if (!memcg)
> + return;
> +
> + res_counter_uncharge(&memcg->kmem, delta);
> + res_counter_uncharge(&memcg->res, delta);
> + if (do_swap_account)
> + res_counter_uncharge(&memcg->memsw, delta);
> +}
> +#endif /* CONFIG_MEMCG_KMEM */
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