- a brief summary of hugetlbpage support in the Linux kernel.
hwpoison.txt
- explains what hwpoison is
+idle_page_tracking.txt
+ - description of the idle page tracking feature.
ksm.txt
- how to use the Kernel Samepage Merging feature.
numa
--- /dev/null
+MOTIVATION
+
+The idle page tracking feature allows to track which memory pages are being
+accessed by a workload and which are idle. This information can be useful for
+estimating the workload's working set size, which, in turn, can be taken into
+account when configuring the workload parameters, setting memory cgroup limits,
+or deciding where to place the workload within a compute cluster.
+
+It is enabled by CONFIG_IDLE_PAGE_TRACKING=y.
+
+USER API
+
+The idle page tracking API is located at /sys/kernel/mm/page_idle. Currently,
+it consists of the only read-write file, /sys/kernel/mm/page_idle/bitmap.
+
+The file implements a bitmap where each bit corresponds to a memory page. The
+bitmap is represented by an array of 8-byte integers, and the page at PFN #i is
+mapped to bit #i%64 of array element #i/64, byte order is native. When a bit is
+set, the corresponding page is idle.
+
+A page is considered idle if it has not been accessed since it was marked idle
+(for more details on what "accessed" actually means see the IMPLEMENTATION
+DETAILS section). To mark a page idle one has to 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 accesses to user memory pages are tracked. These are pages mapped to a
+process address space, page cache and buffer pages, swap cache pages. For other
+page types (e.g. SLAB pages) an attempt to mark a page idle is silently ignored,
+and hence such pages are never reported idle.
+
+For huge pages the idle flag is set only on the head page, so one has to read
+/proc/kpageflags in order to correctly count idle huge pages.
+
+Reading from or writing to /sys/kernel/mm/page_idle/bitmap will return
+-EINVAL if you are not starting the read/write on an 8-byte boundary, or
+if the size of the read/write is not a multiple of 8 bytes. Writing to
+this file beyond max PFN will return -ENXIO.
+
+That said, in order to estimate the amount of pages that are not used by a
+workload one should:
+
+ 1. Mark all the workload's pages as idle by setting corresponding bits in
+ /sys/kernel/mm/page_idle/bitmap. The pages can be found by reading
+ /proc/pid/pagemap if the workload is represented by a process, or by
+ filtering out alien pages using /proc/kpagecgroup in case the workload is
+ placed in a memory cgroup.
+
+ 2. Wait until the workload accesses its working set.
+
+ 3. Read /sys/kernel/mm/page_idle/bitmap and count the number of bits set. If
+ one wants to ignore certain types of pages, e.g. mlocked pages since they
+ are not reclaimable, he or she can filter them out using /proc/kpageflags.
+
+See Documentation/vm/pagemap.txt for more information about /proc/pid/pagemap,
+/proc/kpageflags, and /proc/kpagecgroup.
+
+IMPLEMENTATION DETAILS
+
+The kernel internally keeps track of accesses to user memory pages in order to
+reclaim unreferenced pages first on memory shortage conditions. A page is
+considered referenced if it has been recently accessed via a process address
+space, in which case one or more PTEs it is mapped to will have the Accessed bit
+set, or marked accessed explicitly by the kernel (see mark_page_accessed()). The
+latter happens when:
+
+ - a userspace process reads or writes a page using a system call (e.g. read(2)
+ or write(2))
+
+ - a page that is used for storing filesystem buffers is read or written,
+ because a process needs filesystem metadata stored in it (e.g. lists a
+ directory tree)
+
+ - a page is accessed by a device driver using get_user_pages()
+
+When a dirty page is written to swap or disk as a result of memory reclaim or
+exceeding the dirty memory limit, it is not marked referenced.
+
+The idle memory tracking feature adds a new page flag, the Idle flag. This flag
+is set manually, by writing to /sys/kernel/mm/page_idle/bitmap (see the USER API
+section), and cleared automatically whenever a page is referenced as defined
+above.
+
+When a page is marked idle, the Accessed bit must be cleared in all PTEs it is
+mapped to, otherwise we will not be able to detect accesses to the page coming
+from a process address space. To avoid interference with the reclaimer, which,
+as noted above, uses the Accessed bit to promote actively referenced pages, one
+more page flag is introduced, the Young flag. When the PTE Accessed bit is
+cleared as a result of setting or updating a page's Idle flag, the Young flag
+is set on the page. The reclaimer treats the Young flag as an extra PTE
+Accessed bit and therefore will consider such a page as referenced.
+
+Since the idle memory tracking feature is based on the memory reclaimer logic,
+it only works with pages that are on an LRU list, other pages are silently
+ignored. That means it will ignore a user memory page if it is isolated, but
+since there are usually not many of them, it should not affect the overall
+result noticeably. In order not to stall scanning of the idle page bitmap,
+locked pages may be skipped too.
#include <linux/seq_file.h>
#include <linux/hugetlb.h>
#include <linux/memcontrol.h>
+#include <linux/mmu_notifier.h>
+#include <linux/page_idle.h>
#include <linux/kernel-page-flags.h>
#include <asm/uaccess.h>
#include "internal.h"
#define KPMSIZE sizeof(u64)
#define KPMMASK (KPMSIZE - 1)
+#define KPMBITS (KPMSIZE * BITS_PER_BYTE)
/* /proc/kpagecount - an array exposing page counts
*
#include <linux/swap.h>
#include <linux/swapops.h>
#include <linux/mmu_notifier.h>
+#include <linux/page_idle.h>
#include <asm/elf.h>
#include <asm/uaccess.h>
mss->resident += size;
/* Accumulate the size in pages that have been accessed. */
- if (young || PageReferenced(page))
+ if (young || page_is_young(page) || PageReferenced(page))
mss->referenced += size;
mapcount = page_mapcount(page);
if (mapcount >= 2) {
/* Clear accessed and referenced bits. */
pmdp_test_and_clear_young(vma, addr, pmd);
+ test_and_clear_page_young(page);
ClearPageReferenced(page);
out:
spin_unlock(ptl);
/* Clear accessed and referenced bits. */
ptep_test_and_clear_young(vma, addr, pte);
+ test_and_clear_page_young(page);
ClearPageReferenced(page);
}
pte_unmap_unlock(pte - 1, ptl);
#define ptep_clear_flush_young_notify ptep_clear_flush_young
#define pmdp_clear_flush_young_notify pmdp_clear_flush_young
+#define ptep_clear_young_notify ptep_test_and_clear_young
+#define pmdp_clear_young_notify pmdp_test_and_clear_young
#define ptep_clear_flush_notify ptep_clear_flush
#define pmdp_huge_clear_flush_notify pmdp_huge_clear_flush
#define pmdp_huge_get_and_clear_notify pmdp_huge_get_and_clear
#endif
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
PG_compound_lock,
+#endif
+#if defined(CONFIG_IDLE_PAGE_TRACKING) && defined(CONFIG_64BIT)
+ PG_young,
+ PG_idle,
#endif
__NR_PAGEFLAGS,
#define __PG_HWPOISON 0
#endif
+#if defined(CONFIG_IDLE_PAGE_TRACKING) && defined(CONFIG_64BIT)
+TESTPAGEFLAG(Young, young)
+SETPAGEFLAG(Young, young)
+TESTCLEARFLAG(Young, young)
+PAGEFLAG(Idle, idle)
+#endif
+
/*
* On an anonymous page mapped into a user virtual memory area,
* page->mapping points to its anon_vma, not to a struct address_space;
PAGE_EXT_DEBUG_POISON, /* Page is poisoned */
PAGE_EXT_DEBUG_GUARD,
PAGE_EXT_OWNER,
+#if defined(CONFIG_IDLE_PAGE_TRACKING) && !defined(CONFIG_64BIT)
+ PAGE_EXT_YOUNG,
+ PAGE_EXT_IDLE,
+#endif
};
/*
--- /dev/null
+#ifndef _LINUX_MM_PAGE_IDLE_H
+#define _LINUX_MM_PAGE_IDLE_H
+
+#include <linux/bitops.h>
+#include <linux/page-flags.h>
+#include <linux/page_ext.h>
+
+#ifdef CONFIG_IDLE_PAGE_TRACKING
+
+#ifdef CONFIG_64BIT
+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 bool test_and_clear_page_young(struct page *page)
+{
+ return TestClearPageYoung(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_64BIT */
+/*
+ * If there is not enough space to store Idle and Young bits in page flags, use
+ * page ext flags instead.
+ */
+extern struct page_ext_operations page_idle_ops;
+
+static inline bool page_is_young(struct page *page)
+{
+ return test_bit(PAGE_EXT_YOUNG, &lookup_page_ext(page)->flags);
+}
+
+static inline void set_page_young(struct page *page)
+{
+ set_bit(PAGE_EXT_YOUNG, &lookup_page_ext(page)->flags);
+}
+
+static inline bool test_and_clear_page_young(struct page *page)
+{
+ return test_and_clear_bit(PAGE_EXT_YOUNG,
+ &lookup_page_ext(page)->flags);
+}
+
+static inline bool page_is_idle(struct page *page)
+{
+ return test_bit(PAGE_EXT_IDLE, &lookup_page_ext(page)->flags);
+}
+
+static inline void set_page_idle(struct page *page)
+{
+ set_bit(PAGE_EXT_IDLE, &lookup_page_ext(page)->flags);
+}
+
+static inline void clear_page_idle(struct page *page)
+{
+ clear_bit(PAGE_EXT_IDLE, &lookup_page_ext(page)->flags);
+}
+#endif /* CONFIG_64BIT */
+
+#else /* !CONFIG_IDLE_PAGE_TRACKING */
+
+static inline bool page_is_young(struct page *page)
+{
+ return false;
+}
+
+static inline void set_page_young(struct page *page)
+{
+}
+
+static inline bool test_and_clear_page_young(struct page *page)
+{
+ return false;
+}
+
+static inline bool page_is_idle(struct page *page)
+{
+ return false;
+}
+
+static inline void set_page_idle(struct page *page)
+{
+}
+
+static inline void clear_page_idle(struct page *page)
+{
+}
+
+#endif /* CONFIG_IDLE_PAGE_TRACKING */
+
+#endif /* _LINUX_MM_PAGE_IDLE_H */
processes running early in the lifetime of the systemm until kswapd
finishes the initialisation.
+config IDLE_PAGE_TRACKING
+ bool "Enable idle page tracking"
+ depends on SYSFS && MMU
+ select PAGE_EXTENSION if !64BIT
+ 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/idle_page_tracking.txt for more details.
+
config ZONE_DEVICE
bool "Device memory (pmem, etc...) hotplug support" if EXPERT
default !ZONE_DMA
obj-$(CONFIG_PAGE_EXTENSION) += page_ext.o
obj-$(CONFIG_CMA_DEBUGFS) += cma_debug.o
obj-$(CONFIG_USERFAULTFD) += userfaultfd.o
+obj-$(CONFIG_IDLE_PAGE_TRACKING) += page_idle.o
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
{1UL << PG_compound_lock, "compound_lock" },
#endif
+#if defined(CONFIG_IDLE_PAGE_TRACKING) && defined(CONFIG_64BIT)
+ {1UL << PG_young, "young" },
+ {1UL << PG_idle, "idle" },
+#endif
};
static void dump_flags(unsigned long flags,
#include <linux/migrate.h>
#include <linux/hashtable.h>
#include <linux/userfaultfd_k.h>
+#include <linux/page_idle.h>
#include <asm/tlb.h>
#include <asm/pgalloc.h>
/* clear PageTail before overwriting first_page */
smp_wmb();
+ if (page_is_young(page))
+ set_page_young(page_tail);
+ if (page_is_idle(page))
+ set_page_idle(page_tail);
+
/*
* __split_huge_page_splitting() already set the
* splitting bit in all pmd that could map this
VM_BUG_ON_PAGE(PageLRU(page), page);
/* If there is no mapped pte young don't collapse the page */
- if (pte_young(pteval) || PageReferenced(page) ||
+ if (pte_young(pteval) ||
+ page_is_young(page) || PageReferenced(page) ||
mmu_notifier_test_young(vma->vm_mm, address))
referenced = true;
}
*/
if (page_count(page) != 1 + !!PageSwapCache(page))
goto out_unmap;
- if (pte_young(pteval) || PageReferenced(page) ||
+ if (pte_young(pteval) ||
+ page_is_young(page) || PageReferenced(page) ||
mmu_notifier_test_young(vma->vm_mm, address))
referenced = true;
}
#include <linux/gfp.h>
#include <linux/balloon_compaction.h>
#include <linux/mmu_notifier.h>
+#include <linux/page_idle.h>
#include <asm/tlbflush.h>
__set_page_dirty_nobuffers(newpage);
}
+ if (page_is_young(page))
+ set_page_young(newpage);
+ if (page_is_idle(page))
+ set_page_idle(newpage);
+
/*
* Copy NUMA information to the new page, to prevent over-eager
* future migrations of this same page.
#include <linux/vmalloc.h>
#include <linux/kmemleak.h>
#include <linux/page_owner.h>
+#include <linux/page_idle.h>
/*
* struct page extension
#ifdef CONFIG_PAGE_OWNER
&page_owner_ops,
#endif
+#if defined(CONFIG_IDLE_PAGE_TRACKING) && !defined(CONFIG_64BIT)
+ &page_idle_ops,
+#endif
};
static unsigned long total_usage;
--- /dev/null
+#include <linux/init.h>
+#include <linux/bootmem.h>
+#include <linux/fs.h>
+#include <linux/sysfs.h>
+#include <linux/kobject.h>
+#include <linux/mm.h>
+#include <linux/mmzone.h>
+#include <linux/pagemap.h>
+#include <linux/rmap.h>
+#include <linux/mmu_notifier.h>
+#include <linux/page_ext.h>
+#include <linux/page_idle.h>
+
+#define BITMAP_CHUNK_SIZE sizeof(u64)
+#define BITMAP_CHUNK_BITS (BITMAP_CHUNK_SIZE * BITS_PER_BYTE)
+
+/*
+ * 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 rmap_walk(), 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 *page_idle_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) ||
+ !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;
+}
+
+static int page_idle_clear_pte_refs_one(struct page *page,
+ struct vm_area_struct *vma,
+ unsigned long addr, void *arg)
+{
+ struct mm_struct *mm = vma->vm_mm;
+ spinlock_t *ptl;
+ pmd_t *pmd;
+ pte_t *pte;
+ bool referenced = false;
+
+ if (unlikely(PageTransHuge(page))) {
+ pmd = page_check_address_pmd(page, mm, addr,
+ PAGE_CHECK_ADDRESS_PMD_FLAG, &ptl);
+ if (pmd) {
+ referenced = pmdp_clear_young_notify(vma, addr, pmd);
+ spin_unlock(ptl);
+ }
+ } else {
+ pte = page_check_address(page, mm, addr, &ptl, 0);
+ if (pte) {
+ referenced = ptep_clear_young_notify(vma, addr, pte);
+ pte_unmap_unlock(pte, ptl);
+ }
+ }
+ if (referenced) {
+ clear_page_idle(page);
+ /*
+ * We cleared the referenced bit in a mapping to this page. To
+ * avoid interference with page reclaim, mark it young so that
+ * page_referenced() will return > 0.
+ */
+ set_page_young(page);
+ }
+ return SWAP_AGAIN;
+}
+
+static void page_idle_clear_pte_refs(struct page *page)
+{
+ /*
+ * Since rwc.arg is unused, rwc is effectively immutable, so we
+ * can make it static const to save some cycles and stack.
+ */
+ static const struct rmap_walk_control rwc = {
+ .rmap_one = page_idle_clear_pte_refs_one,
+ .anon_lock = page_lock_anon_vma_read,
+ };
+ bool need_lock;
+
+ if (!page_mapped(page) ||
+ !page_rmapping(page))
+ return;
+
+ need_lock = !PageAnon(page) || PageKsm(page);
+ if (need_lock && !trylock_page(page))
+ return;
+
+ rmap_walk(page, (struct rmap_walk_control *)&rwc);
+
+ if (need_lock)
+ unlock_page(page);
+}
+
+static ssize_t page_idle_bitmap_read(struct file *file, struct kobject *kobj,
+ struct bin_attribute *attr, char *buf,
+ loff_t pos, size_t count)
+{
+ u64 *out = (u64 *)buf;
+ struct page *page;
+ unsigned long pfn, end_pfn;
+ int bit;
+
+ if (pos % BITMAP_CHUNK_SIZE || count % BITMAP_CHUNK_SIZE)
+ return -EINVAL;
+
+ pfn = pos * 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, BITMAP_CHUNK_BITS);
+
+ for (; pfn < end_pfn; pfn++) {
+ bit = pfn % BITMAP_CHUNK_BITS;
+ if (!bit)
+ *out = 0ULL;
+ page = page_idle_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.
+ */
+ page_idle_clear_pte_refs(page);
+ if (page_is_idle(page))
+ *out |= 1ULL << bit;
+ }
+ put_page(page);
+ }
+ if (bit == BITMAP_CHUNK_BITS - 1)
+ out++;
+ cond_resched();
+ }
+ return (char *)out - buf;
+}
+
+static ssize_t page_idle_bitmap_write(struct file *file, struct kobject *kobj,
+ struct bin_attribute *attr, char *buf,
+ loff_t pos, size_t count)
+{
+ const u64 *in = (u64 *)buf;
+ struct page *page;
+ unsigned long pfn, end_pfn;
+ int bit;
+
+ if (pos % BITMAP_CHUNK_SIZE || count % BITMAP_CHUNK_SIZE)
+ return -EINVAL;
+
+ pfn = pos * 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, BITMAP_CHUNK_BITS);
+
+ for (; pfn < end_pfn; pfn++) {
+ bit = pfn % BITMAP_CHUNK_BITS;
+ if ((*in >> bit) & 1) {
+ page = page_idle_get_page(pfn);
+ if (page) {
+ page_idle_clear_pte_refs(page);
+ set_page_idle(page);
+ put_page(page);
+ }
+ }
+ if (bit == BITMAP_CHUNK_BITS - 1)
+ in++;
+ cond_resched();
+ }
+ return (char *)in - buf;
+}
+
+static struct bin_attribute page_idle_bitmap_attr =
+ __BIN_ATTR(bitmap, S_IRUSR | S_IWUSR,
+ page_idle_bitmap_read, page_idle_bitmap_write, 0);
+
+static struct bin_attribute *page_idle_bin_attrs[] = {
+ &page_idle_bitmap_attr,
+ NULL,
+};
+
+static struct attribute_group page_idle_attr_group = {
+ .bin_attrs = page_idle_bin_attrs,
+ .name = "page_idle",
+};
+
+#ifndef CONFIG_64BIT
+static bool need_page_idle(void)
+{
+ return true;
+}
+struct page_ext_operations page_idle_ops = {
+ .need = need_page_idle,
+};
+#endif
+
+static int __init page_idle_init(void)
+{
+ int err;
+
+ err = sysfs_create_group(mm_kobj, &page_idle_attr_group);
+ if (err) {
+ pr_err("page_idle: register sysfs failed\n");
+ return err;
+ }
+ return 0;
+}
+subsys_initcall(page_idle_init);
#include <linux/migrate.h>
#include <linux/hugetlb.h>
#include <linux/backing-dev.h>
+#include <linux/page_idle.h>
#include <asm/tlbflush.h>
pte_unmap_unlock(pte, ptl);
}
+ if (referenced)
+ clear_page_idle(page);
+ if (test_and_clear_page_young(page))
+ referenced++;
+
if (referenced) {
pra->referenced++;
pra->vm_flags |= vma->vm_flags;
#include <linux/gfp.h>
#include <linux/uio.h>
#include <linux/hugetlb.h>
+#include <linux/page_idle.h>
#include "internal.h"
} else if (!PageReferenced(page)) {
SetPageReferenced(page);
}
+ if (page_is_idle(page))
+ clear_page_idle(page);
}
EXPORT_SYMBOL(mark_page_accessed);
projects / cascardo / linux.git / commitdiff