On Tue, Mar 09, 2021 at 06:07:15PM +0800, Muchun Song wrote:
> We want to reuse the obj_cgroup APIs to charge the kmem pages.
> If we do that, we should store an object cgroup pointer to
> page->memcg_data for the kmem pages.
>
> Finally, page->memcg_data can have 3 different meanings.
>
> 1) For the slab pages, page->memcg_data points to an object cgroups
> vector.
>
> 2) For the kmem pages (exclude the slab pages), page->memcg_data
> points to an object cgroup.
>
> 3) For the user pages (e.g. the LRU pages), page->memcg_data points
> to a memory cgroup.
>
> Currently we always get the memory cgroup associated with a page via
> page_memcg() or page_memcg_rcu(). page_memcg_check() is special, it
> has to be used in cases when it's not known if a page has an
> associated memory cgroup pointer or an object cgroups vector. Because
> the page->memcg_data of the kmem page is not pointing to a memory
> cgroup in the later patch, the page_memcg() and page_memcg_rcu()
> cannot be applicable for the kmem pages. In this patch, make
> page_memcg() and page_memcg_rcu() no longer apply to the kmem pages.
> We do not change the behavior of the page_memcg_check(), it is also
> applicable for the kmem pages.
>
> In the end, there are 3 helpers to get the memcg associated with a page.
> Usage is as follows.
>
> 1) Get the memory cgroup associated with a non-kmem page (e.g. the LRU
> pages).
>
> - page_memcg()
> - page_memcg_rcu()
>
> 2) Get the memory cgroup associated with a page. It has to be used in
> cases when it's not known if a page has an associated memory cgroup
> pointer or an object cgroups vector. Returns NULL for slab pages or
> uncharged pages. Otherwise, returns memory cgroup for charged pages
> (e.g. the kmem pages, the LRU pages).
>
> - page_memcg_check()
>
> In some place, we use page_memcg() to check whether the page is charged.
> Now introduce page_memcg_charged() helper to do that.
>
> This is a preparation for reparenting the kmem pages.
>
> Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
> ---
> include/linux/memcontrol.h | 33 +++++++++++++++++++++++++++------
> mm/memcontrol.c | 23 +++++++++++++----------
> mm/page_alloc.c | 4 ++--
> 3 files changed, 42 insertions(+), 18 deletions(-)
>
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index e6dc793d587d..83cbcdcfcc92 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -358,14 +358,26 @@ enum page_memcg_data_flags {
>
> #define MEMCG_DATA_FLAGS_MASK (__NR_MEMCG_DATA_FLAGS - 1)
>
> +/* Return true for charged page, otherwise false. */
> +static inline bool page_memcg_charged(struct page *page)
> +{
> + unsigned long memcg_data = page->memcg_data;
> +
> + VM_BUG_ON_PAGE(PageSlab(page), page);
> + VM_BUG_ON_PAGE(memcg_data & MEMCG_DATA_OBJCGS, page);
> +
> + return !!memcg_data;
> +}
> +
> /*
> - * page_memcg - get the memory cgroup associated with a page
> + * page_memcg - get the memory cgroup associated with a non-kmem page
> * @page: a pointer to the page struct
> *
> * Returns a pointer to the memory cgroup associated with the page,
> * or NULL. This function assumes that the page is known to have a
> * proper memory cgroup pointer. It's not safe to call this function
> - * against some type of pages, e.g. slab pages or ex-slab pages.
> + * against some type of pages, e.g. slab pages, kmem pages or ex-slab
> + * pages.
> *
> * Any of the following ensures page and memcg binding stability:
> * - the page lock
> @@ -378,27 +390,31 @@ static inline struct mem_cgroup *page_memcg(struct page *page)
> unsigned long memcg_data = page->memcg_data;
>
> VM_BUG_ON_PAGE(PageSlab(page), page);
> + VM_BUG_ON_PAGE(memcg_data & MEMCG_DATA_KMEM, page);
> VM_BUG_ON_PAGE(memcg_data & MEMCG_DATA_OBJCGS, page);
>
> return (struct mem_cgroup *)(memcg_data & ~MEMCG_DATA_FLAGS_MASK);
> }
>
> /*
> - * page_memcg_rcu - locklessly get the memory cgroup associated with a page
> + * page_memcg_rcu - locklessly get the memory cgroup associated with a non-kmem page
> * @page: a pointer to the page struct
> *
> * Returns a pointer to the memory cgroup associated with the page,
> * or NULL. This function assumes that the page is known to have a
> * proper memory cgroup pointer. It's not safe to call this function
> - * against some type of pages, e.g. slab pages or ex-slab pages.
> + * against some type of pages, e.g. slab pages, kmem pages or ex-slab
> + * pages.
> */
> static inline struct mem_cgroup *page_memcg_rcu(struct page *page)
> {
> + unsigned long memcg_data = READ_ONCE(page->memcg_data);
> +
> VM_BUG_ON_PAGE(PageSlab(page), page);
> + VM_BUG_ON_PAGE(memcg_data & MEMCG_DATA_KMEM, page);
> WARN_ON_ONCE(!rcu_read_lock_held());
>
> - return (struct mem_cgroup *)(READ_ONCE(page->memcg_data) &
> - ~MEMCG_DATA_FLAGS_MASK);
> + return (struct mem_cgroup *)(memcg_data & ~MEMCG_DATA_FLAGS_MASK);
> }
>
> /*
> @@ -1072,6 +1088,11 @@ void mem_cgroup_split_huge_fixup(struct page *head);
>
> struct mem_cgroup;
>
> +static inline bool page_memcg_charged(struct page *page)
> +{
> + return false;
> +}
> +
> static inline struct mem_cgroup *page_memcg(struct page *page)
> {
> return NULL;
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index fc22da9805fb..e1dc73ceb98a 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -855,10 +855,11 @@ void __mod_lruvec_page_state(struct page *page, enum node_stat_item idx,
> int val)
> {
> struct page *head = compound_head(page); /* rmap on tail pages */
> - struct mem_cgroup *memcg = page_memcg(head);
> + struct mem_cgroup *memcg;
> pg_data_t *pgdat = page_pgdat(page);
> struct lruvec *lruvec;
>
> + memcg = page_memcg_check(head);
In general, this and the next patch look good to me (aside from some small things,
commented separately).
But I wonder if it's better to have two separate versions of __mod_lruvec_page_state()
for kmem and non-kmem pages, rather then rely on PageMemcgKmem flag. It's a hot path,
so if we can have fewer conditions here, that would be nice.
I take a brief look (and could be wrong), but it seems like we know in advance
which version should be used.
Thanks!
> /* Untracked pages have no memcg, no lruvec. Update only the node */
> if (!memcg) {
> __mod_node_page_state(pgdat, idx, val);
> @@ -3166,12 +3167,13 @@ int __memcg_kmem_charge_page(struct page *page, gfp_t gfp, int order)
> */
> void __memcg_kmem_uncharge_page(struct page *page, int order)
> {
> - struct mem_cgroup *memcg = page_memcg(page);
> + struct mem_cgroup *memcg;
> unsigned int nr_pages = 1 << order;
>
> - if (!memcg)
> + if (!page_memcg_charged(page))
> return;
>
> + memcg = page_memcg_check(page);
> VM_BUG_ON_PAGE(mem_cgroup_is_root(memcg), page);
> __memcg_kmem_uncharge(memcg, nr_pages);
> page->memcg_data = 0;
> @@ -6827,24 +6829,25 @@ static void uncharge_batch(const struct uncharge_gather *ug)
> static void uncharge_page(struct page *page, struct uncharge_gather *ug)
> {
> unsigned long nr_pages;
> + struct mem_cgroup *memcg;
>
> VM_BUG_ON_PAGE(PageLRU(page), page);
>
> - if (!page_memcg(page))
> + if (!page_memcg_charged(page))
> return;
>
> /*
> * Nobody should be changing or seriously looking at
> - * page_memcg(page) at this point, we have fully
> - * exclusive access to the page.
> + * page memcg at this point, we have fully exclusive
> + * access to the page.
> */
> -
> - if (ug->memcg != page_memcg(page)) {
> + memcg = page_memcg_check(page);
> + if (ug->memcg != memcg) {
> if (ug->memcg) {
> uncharge_batch(ug);
> uncharge_gather_clear(ug);
> }
> - ug->memcg = page_memcg(page);
> + ug->memcg = memcg;
>
> /* pairs with css_put in uncharge_batch */
> css_get(&ug->memcg->css);
> @@ -6877,7 +6880,7 @@ void mem_cgroup_uncharge(struct page *page)
> return;
>
> /* Don't touch page->lru of any random page, pre-check: */
> - if (!page_memcg(page))
> + if (!page_memcg_charged(page))
> return;
>
> uncharge_gather_clear(&ug);
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index f10966e3b4a5..bcb58ae15e24 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1124,7 +1124,7 @@ static inline bool page_expected_state(struct page *page,
> if (unlikely((unsigned long)page->mapping |
> page_ref_count(page) |
> #ifdef CONFIG_MEMCG
> - (unsigned long)page_memcg(page) |
> + page_memcg_charged(page) |
> #endif
> (page->flags & check_flags)))
> return false;
> @@ -1149,7 +1149,7 @@ static const char *page_bad_reason(struct page *page, unsigned long flags)
> bad_reason = "PAGE_FLAGS_CHECK_AT_FREE flag(s) set";
> }
> #ifdef CONFIG_MEMCG
> - if (unlikely(page_memcg(page)))
> + if (unlikely(page_memcg_charged(page)))
> bad_reason = "page still charged to cgroup";
> #endif
> return bad_reason;
> --
> 2.11.0
>
