Messages in this thread | | | Date | Mon, 31 Jan 2022 16:43:32 -0500 | Subject | Re: [PATCH v3 3/4] mm/page_owner: Print memcg information | From | Waiman Long <> |
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On 1/31/22 15:51, Mike Rapoport wrote: > On Mon, Jan 31, 2022 at 02:23:07PM -0500, Waiman Long wrote: >> It was found that a number of offlined memcgs were not freed because >> they were pinned by some charged pages that were present. Even "echo >> 1 > /proc/sys/vm/drop_caches" wasn't able to free those pages. These >> offlined but not freed memcgs tend to increase in number over time with >> the side effect that percpu memory consumption as shown in /proc/meminfo >> also increases over time. >> >> In order to find out more information about those pages that pin >> offlined memcgs, the page_owner feature is extended to print memory >> cgroup information especially whether the cgroup is offlined or not. >> >> Signed-off-by: Waiman Long <longman@redhat.com> >> Acked-by: David Rientjes <rientjes@google.com> >> --- >> mm/page_owner.c | 39 +++++++++++++++++++++++++++++++++++++++ >> 1 file changed, 39 insertions(+) >> >> diff --git a/mm/page_owner.c b/mm/page_owner.c >> index 28dac73e0542..a471c74c7fe0 100644 >> --- a/mm/page_owner.c >> +++ b/mm/page_owner.c >> @@ -10,6 +10,7 @@ >> #include <linux/migrate.h> >> #include <linux/stackdepot.h> >> #include <linux/seq_file.h> >> +#include <linux/memcontrol.h> >> #include <linux/sched/clock.h> >> >> #include "internal.h" >> @@ -325,6 +326,42 @@ void pagetypeinfo_showmixedcount_print(struct seq_file *m, >> seq_putc(m, '\n'); >> } >> >> +#ifdef CONFIG_MEMCG >> +/* >> + * Looking for memcg information and print it out >> + */ >> +static inline void print_page_owner_memcg(char *kbuf, size_t count, int *pret, >> + struct page *page) >> +{ >> + unsigned long memcg_data = READ_ONCE(page->memcg_data); >> + struct mem_cgroup *memcg; >> + bool onlined; >> + char name[80]; >> + >> + if (!memcg_data) >> + return; >> + >> + if (memcg_data & MEMCG_DATA_OBJCGS) >> + *pret += scnprintf(kbuf + *pret, count - *pret, >> + "Slab cache page\n"); > Don't we need to check for overflow here?
See my previous patch 2 and the reason I used scnprintf() is that it never return a length that is >= the given size. So overflow won't happen. The final snprintf() in print_page_owner() will detect buffer overflow.
> >> + >> + memcg = page_memcg_check(page); >> + if (!memcg) >> + return; >> + >> + onlined = (memcg->css.flags & CSS_ONLINE); >> + cgroup_name(memcg->css.cgroup, name, sizeof(name)); >> + *pret += scnprintf(kbuf + *pret, count - *pret, >> + "Charged %sto %smemcg %s\n", >> + PageMemcgKmem(page) ? "(via objcg) " : "", >> + onlined ? "" : "offlined ", >> + name); > Ditto > >> +} >> +#else /* CONFIG_MEMCG */ >> +static inline void print_page_owner_memcg(char *kbuf, size_t count, int *pret, >> + struct page *page) { } > I think #ifdef inside the print_page_owner_memcg() functions will be > simpler and clearer. Yes, I see both styles used in kernel code though this style is probably more common. I will keep this unless there is a good reason to do otherwise. > >> +#endif /* CONFIG_MEMCG */ >> + >> static ssize_t >> print_page_owner(char __user *buf, size_t count, unsigned long pfn, >> struct page *page, struct page_owner *page_owner, >> @@ -365,6 +402,8 @@ print_page_owner(char __user *buf, size_t count, unsigned long pfn, >> migrate_reason_names[page_owner->last_migrate_reason]); >> } >> >> + print_page_owner_memcg(kbuf, count, &ret, page); >> + > ret can go over count here. > Why not make print_page_owner_memcg() an int so that the call will be > consistent with other calls in print_page_owner(): > > ret += print_page_owner_memcg(kbuf, count, page); > if (ret >= count) > goto err;
See my comments above.
Cheers, Longman
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