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Subject[PATCH -mm v7 6/6] proc: export idle flag via kpageflags
Date
As noted by Minchan, a benefit of reading idle flag from
/proc/kpageflags is that one can easily filter dirty and/or unevictable
pages while estimating the size of unused memory.

Note that idle flag read from /proc/kpageflags may be stale in case the
page was accessed via a PTE, because it would be too costly to iterate
over all page mappings on each /proc/kpageflags read to provide an
up-to-date value. To make sure the flag is up-to-date one has to read
/proc/kpageidle first.

Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>
---
Documentation/vm/pagemap.txt | 6 ++++++
fs/proc/page.c | 3 +++
include/uapi/linux/kernel-page-flags.h | 1 +
3 files changed, 10 insertions(+)

diff --git a/Documentation/vm/pagemap.txt b/Documentation/vm/pagemap.txt
index c9266340852c..5896b7d7fd74 100644
--- a/Documentation/vm/pagemap.txt
+++ b/Documentation/vm/pagemap.txt
@@ -64,6 +64,7 @@ There are five components to pagemap:
22. THP
23. BALLOON
24. ZERO_PAGE
+ 25. IDLE

* /proc/kpagecgroup. This file contains a 64-bit inode number of the
memory cgroup each page is charged to, indexed by PFN. Only available when
@@ -124,6 +125,11 @@ Short descriptions to the page flags:
24. ZERO_PAGE
zero page for pfn_zero or huge_zero page

+25. IDLE
+ page has not been accessed since it was marked idle (see /proc/kpageidle)
+ Note that this flag may be stale in case the page was accessed via a PTE.
+ To make sure the flag is up-to-date one has to read /proc/kpageidle first.
+
[IO related page flags]
1. ERROR IO error occurred
3. UPTODATE page has up-to-date data
diff --git a/fs/proc/page.c b/fs/proc/page.c
index e51690c5f173..4fa4eadfd30e 100644
--- a/fs/proc/page.c
+++ b/fs/proc/page.c
@@ -149,6 +149,9 @@ u64 stable_page_flags(struct page *page)
if (PageBalloon(page))
u |= 1 << KPF_BALLOON;

+ if (page_is_idle(page))
+ u |= 1 << KPF_IDLE;
+
u |= kpf_copy_bit(k, KPF_LOCKED, PG_locked);

u |= kpf_copy_bit(k, KPF_SLAB, PG_slab);
diff --git a/include/uapi/linux/kernel-page-flags.h b/include/uapi/linux/kernel-page-flags.h
index a6c4962e5d46..5da5f8751ce7 100644
--- a/include/uapi/linux/kernel-page-flags.h
+++ b/include/uapi/linux/kernel-page-flags.h
@@ -33,6 +33,7 @@
#define KPF_THP 22
#define KPF_BALLOON 23
#define KPF_ZERO_PAGE 24
+#define KPF_IDLE 25


#endif /* _UAPILINUX_KERNEL_PAGE_FLAGS_H */
--
2.1.4


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