[Devel] [PATCH rh7 v2 3/3] proc: add kpageidle file
Vladimir Davydov
vdavydov at parallels.com
Mon May 18 04:33:34 PDT 2015
Knowing the portion of memory that is not used by a certain application
or memory cgroup (idle memory) can be useful for partitioning the system
efficiently, e.g. by setting memory cgroup limits appropriately.
Currently, the only means to estimate the amount of idle memory provided
by the kernel is /proc/PID/{clear_refs,smaps}: the user can clear the
access bit for all pages mapped to a particular process by writing 1 to
clear_refs, wait for some time, and then count smaps:Referenced.
However, this method has two serious shortcomings:
- it does not count unmapped file pages
- it affects the reclaimer logic
To overcome these drawbacks, this patch introduces two new page flags,
Idle and Young, and a new proc file, /proc/kpageidle. A page's Idle flag
can only be set from userspace by setting bit in /proc/kpageidle at the
offset corresponding to the page, and it is cleared whenever the page is
accessed either through page tables (it is cleared in page_referenced()
in this case) or using the read(2) system call (mark_page_accessed()).
Thus by setting the Idle flag for pages of a particular workload, which
can be found e.g. by reading /proc/PID/pagemap, waiting for some time to
let the workload access its working set, and then reading the kpageidle
file, one can estimate the amount of pages that are not used by the
workload.
The Young page flag is used to avoid interference with the memory
reclaimer. A page's Young flag is set whenever the Access bit of a page
table entry pointing to the page is cleared by writing to kpageidle. If
page_referenced() is called on a Young page, it will add 1 to its return
value, therefore concealing the fact that the Access bit was cleared.
Note, since there is no room for extra page flags on 32 bit, this
feature uses extended page flags when compiled on 32 bit.
(on RH7 page ext is not available so make it depend on 64 bit)
Signed-off-by: Vladimir Davydov <vdavydov at parallels.com>
---
Documentation/vm/pagemap.txt | 12 ++-
fs/proc/page.c | 168 ++++++++++++++++++++++++++++++++++++++++++
fs/proc/task_mmu.c | 3 +-
include/linux/mm.h | 50 +++++++++++++
include/linux/page-flags.h | 9 +++
mm/Kconfig | 12 +++
mm/page_alloc.c | 4 +
mm/rmap.c | 9 +++
mm/swap.c | 2 +
9 files changed, 267 insertions(+), 2 deletions(-)
diff --git a/Documentation/vm/pagemap.txt b/Documentation/vm/pagemap.txt
index e37cff950ae8..a4fe9b25a6c9 100644
--- a/Documentation/vm/pagemap.txt
+++ b/Documentation/vm/pagemap.txt
@@ -5,7 +5,7 @@ pagemap is a new (as of 2.6.25) set of interfaces in the kernel that allow
userspace programs to examine the page tables and related information by
reading files in /proc.
-There are four components to pagemap:
+There are five components to pagemap:
* /proc/pid/pagemap. This file lets a userspace process find out which
physical frame each virtual page is mapped to. It contains one 64-bit
@@ -67,6 +67,16 @@ There are four components to pagemap:
memory cgroup each page is charged to, indexed by PFN. Only available when
CONFIG_MEMCG is set.
+ * /proc/kpageidle. This file implements a bitmap where each bit corresponds
+ to a page, indexed by PFN. When the bit is set, the corresponding page is
+ idle. A page is considered idle if it has not been accessed since it was
+ marked idle. To mark a page idle one should set the bit corresponding to the
+ page by writing to the file. A value written to the file is OR-ed with the
+ current bitmap value. Only user memory pages can be marked idle, for other
+ page types input is silently ignored. Writing to this file beyond max PFN
+ results in the ENXIO error. Only available when CONFIG_IDLE_PAGE_TRACKING is
+ set.
+
Short descriptions to the page flags:
0. LOCKED
diff --git a/fs/proc/page.c b/fs/proc/page.c
index c9cbed32be43..49aebd2e3596 100644
--- a/fs/proc/page.c
+++ b/fs/proc/page.c
@@ -15,6 +15,7 @@
#define KPMSIZE sizeof(u64)
#define KPMMASK (KPMSIZE - 1)
+#define KPMBITS (KPMSIZE * BITS_PER_BYTE)
/* /proc/kpagecount - an array exposing page counts
*
@@ -263,6 +264,169 @@ static const struct file_operations proc_kpagecgroup_operations = {
};
#endif /* CONFIG_MEMCG */
+#ifdef CONFIG_IDLE_PAGE_TRACKING
+/*
+ * Idle page tracking only considers user memory pages, for other types of
+ * pages the idle flag is always unset and an attempt to set it is silently
+ * ignored.
+ *
+ * We treat a page as a user memory page if it is on an LRU list, because it is
+ * always safe to pass such a page to page_referenced(), which is essential for
+ * idle page tracking. With such an indicator of user pages we can skip
+ * isolated pages, but since there are not usually many of them, it will hardly
+ * affect the overall result.
+ *
+ * This function tries to get a user memory page by pfn as described above.
+ */
+static struct page *kpageidle_get_page(unsigned long pfn)
+{
+ struct page *page;
+ struct zone *zone;
+
+ if (!pfn_valid(pfn))
+ return NULL;
+
+ page = pfn_to_page(pfn);
+ if (!page || !PageLRU(page))
+ return NULL;
+ if (!get_page_unless_zero(page))
+ return NULL;
+
+ zone = page_zone(page);
+ spin_lock_irq(&zone->lru_lock);
+ if (unlikely(!PageLRU(page))) {
+ put_page(page);
+ page = NULL;
+ }
+ spin_unlock_irq(&zone->lru_lock);
+ return page;
+}
+
+/*
+ * This function calls page_referenced() to clear the referenced bit for all
+ * mappings to a page. Since the latter also clears the page idle flag if the
+ * page was referenced, it can be used to update the idle flag of a page.
+ */
+static void kpageidle_clear_pte_refs(struct page *page)
+{
+ unsigned long dummy;
+
+ if (page_referenced(page, 0, NULL, &dummy))
+ /*
+ * We cleared the referenced bit in a mapping to this page. To
+ * avoid interference with the reclaimer, mark it young so that
+ * the next call to page_referenced() will also return > 0 (see
+ * page_referenced_one())
+ */
+ set_page_young(page);
+}
+
+static ssize_t kpageidle_read(struct file *file, char __user *buf,
+ size_t count, loff_t *ppos)
+{
+ u64 __user *out = (u64 __user *)buf;
+ struct page *page;
+ unsigned long pfn, end_pfn;
+ ssize_t ret = 0;
+ u64 idle_bitmap = 0;
+ int bit;
+
+ if (*ppos & KPMMASK || count & KPMMASK)
+ return -EINVAL;
+
+ pfn = *ppos * BITS_PER_BYTE;
+ if (pfn >= max_pfn)
+ return 0;
+
+ end_pfn = pfn + count * BITS_PER_BYTE;
+ if (end_pfn > max_pfn)
+ end_pfn = ALIGN(max_pfn, KPMBITS);
+
+ for (; pfn < end_pfn; pfn++) {
+ bit = pfn % KPMBITS;
+ page = kpageidle_get_page(pfn);
+ if (page) {
+ if (page_is_idle(page)) {
+ /*
+ * The page might have been referenced via a
+ * pte, in which case it is not idle. Clear
+ * refs and recheck.
+ */
+ kpageidle_clear_pte_refs(page);
+ if (page_is_idle(page))
+ idle_bitmap |= 1ULL << bit;
+ }
+ put_page(page);
+ }
+ if (bit == KPMBITS - 1) {
+ if (put_user(idle_bitmap, out)) {
+ ret = -EFAULT;
+ break;
+ }
+ idle_bitmap = 0;
+ out++;
+ }
+ }
+
+ *ppos += (char __user *)out - buf;
+ if (!ret)
+ ret = (char __user *)out - buf;
+ return ret;
+}
+
+static ssize_t kpageidle_write(struct file *file, const char __user *buf,
+ size_t count, loff_t *ppos)
+{
+ const u64 __user *in = (const u64 __user *)buf;
+ struct page *page;
+ unsigned long pfn, end_pfn;
+ ssize_t ret = 0;
+ u64 idle_bitmap = 0;
+ int bit;
+
+ if (*ppos & KPMMASK || count & KPMMASK)
+ return -EINVAL;
+
+ pfn = *ppos * BITS_PER_BYTE;
+ if (pfn >= max_pfn)
+ return -ENXIO;
+
+ end_pfn = pfn + count * BITS_PER_BYTE;
+ if (end_pfn > max_pfn)
+ end_pfn = ALIGN(max_pfn, KPMBITS);
+
+ for (; pfn < end_pfn; pfn++) {
+ bit = pfn % KPMBITS;
+ if (bit == 0) {
+ if (get_user(idle_bitmap, in)) {
+ ret = -EFAULT;
+ break;
+ }
+ in++;
+ }
+ if (idle_bitmap >> bit & 1) {
+ page = kpageidle_get_page(pfn);
+ if (page) {
+ kpageidle_clear_pte_refs(page);
+ set_page_idle(page);
+ put_page(page);
+ }
+ }
+ }
+
+ *ppos += (const char __user *)in - buf;
+ if (!ret)
+ ret = (const char __user *)in - buf;
+ return ret;
+}
+
+static const struct file_operations proc_kpageidle_operations = {
+ .llseek = mem_lseek,
+ .read = kpageidle_read,
+ .write = kpageidle_write,
+};
+#endif /* CONFIG_IDLE_PAGE_TRACKING */
+
static int __init proc_page_init(void)
{
proc_create("kpagecount", S_IRUSR, NULL, &proc_kpagecount_operations);
@@ -270,6 +434,10 @@ static int __init proc_page_init(void)
#ifdef CONFIG_MEMCG
proc_create("kpagecgroup", S_IRUSR, NULL, &proc_kpagecgroup_operations);
#endif
+#ifdef CONFIG_IDLE_PAGE_TRACKING
+ proc_create("kpageidle", S_IRUSR | S_IWUSR, NULL,
+ &proc_kpageidle_operations);
+#endif
return 0;
}
module_init(proc_page_init);
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 86cba128f23c..49ef0e109133 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -482,7 +482,7 @@ static void smaps_pte_entry(pte_t ptent, unsigned long addr,
mss->resident += ptent_size;
/* Accumulate the size in pages that have been accessed. */
- if (pte_young(ptent) || PageReferenced(page))
+ if (pte_young(ptent) || page_is_young(page) || PageReferenced(page))
mss->referenced += ptent_size;
mapcount = page_mapcount(page);
if (mapcount >= 2) {
@@ -778,6 +778,7 @@ static int clear_refs_pte_range(pmd_t *pmd, unsigned long addr,
/* Clear accessed and referenced bits. */
ptep_test_and_clear_young(vma, addr, pte);
+ clear_page_young(page);
ClearPageReferenced(page);
}
pte_unmap_unlock(pte - 1, ptl);
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 3dfdc2b4b7e6..f641f9f5554e 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2029,5 +2029,55 @@ void __init setup_nr_node_ids(void);
static inline void setup_nr_node_ids(void) {}
#endif
+#ifdef CONFIG_IDLE_PAGE_TRACKING
+static inline bool page_is_young(struct page *page)
+{
+ return PageYoung(page);
+}
+
+static inline void set_page_young(struct page *page)
+{
+ SetPageYoung(page);
+}
+
+static inline void clear_page_young(struct page *page)
+{
+ ClearPageYoung(page);
+}
+
+static inline bool page_is_idle(struct page *page)
+{
+ return PageIdle(page);
+}
+
+static inline void set_page_idle(struct page *page)
+{
+ SetPageIdle(page);
+}
+
+static inline void clear_page_idle(struct page *page)
+{
+ ClearPageIdle(page);
+}
+#else /* !CONFIG_IDLE_PAGE_TRACKING */
+static inline bool page_is_young(struct page *page)
+{
+ return false;
+}
+
+static inline void clear_page_young(struct page *page)
+{
+}
+
+static inline bool page_is_idle(struct page *page)
+{
+ return false;
+}
+
+static inline void clear_page_idle(struct page *page)
+{
+}
+#endif /* CONFIG_IDLE_PAGE_TRACKING */
+
#endif /* __KERNEL__ */
#endif /* _LINUX_MM_H */
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 6d53675c2b54..67da013c6888 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -109,6 +109,10 @@ enum pageflags {
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
PG_compound_lock,
#endif
+#ifdef CONFIG_IDLE_PAGE_TRACKING
+ PG_young,
+ PG_idle,
+#endif
__NR_PAGEFLAGS,
/* Filesystems */
@@ -275,6 +279,11 @@ PAGEFLAG_FALSE(HWPoison)
#define __PG_HWPOISON 0
#endif
+#ifdef CONFIG_IDLE_PAGE_TRACKING
+PAGEFLAG(Young, young)
+PAGEFLAG(Idle, idle)
+#endif
+
u64 stable_page_flags(struct page *page);
static inline int PageUptodate(struct page *page)
diff --git a/mm/Kconfig b/mm/Kconfig
index e3c7f58c8484..3dd1af92016d 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -541,3 +541,15 @@ config TSWAP
stores reclaimed pages in memory without any modifications. It is
only worth enabling if used along with memory cgroups in order to
cache pages which were reclaimed on local pressure.
+
+config IDLE_PAGE_TRACKING
+ bool "Enable idle page tracking"
+ depends on 64BIT
+ select PROC_PAGE_MONITOR
+ help
+ This feature allows to estimate the amount of user pages that have
+ not been touched during a given period of time. This information can
+ be useful to tune memory cgroup limits and/or for job placement
+ within a compute cluster.
+
+ See Documentation/vm/pagemap.txt for more details.
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 119005d94651..cd26308da1a5 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -6361,6 +6361,10 @@ static const struct trace_print_flags pageflag_names[] = {
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
{1UL << PG_compound_lock, "compound_lock" },
#endif
+#ifdef CONFIG_IDLE_PAGE_TRACKING
+ {1UL << PG_young, "young" },
+ {1UL << PG_idle, "idle" },
+#endif
};
static void dump_page_flags(unsigned long flags)
diff --git a/mm/rmap.c b/mm/rmap.c
index 85562949312e..fa823bed3c66 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -727,6 +727,15 @@ int page_referenced_one(struct page *page, struct vm_area_struct *vma,
pte_unmap_unlock(pte, ptl);
}
+ if (referenced && page_is_idle(page))
+ clear_page_idle(page);
+
+ if (page_is_young(page)) {
+ clear_page_young(page);
+ if (!referenced)
+ referenced++;
+ }
+
(*mapcount)--;
if (referenced)
diff --git a/mm/swap.c b/mm/swap.c
index 4ce3c1e2a44f..27fcb8ad207f 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -487,6 +487,8 @@ void mark_page_accessed(struct page *page)
} else if (!PageReferenced(page)) {
SetPageReferenced(page);
}
+ if (page_is_idle(page))
+ clear_page_idle(page);
}
EXPORT_SYMBOL(mark_page_accessed);
--
1.7.10.4
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