Idle page tracking currently does not work well in the following
scenario:
1. mark page-A idle which was present at that time.
2. run workload
3. page-A is not touched by workload
4. *sudden* memory pressure happen so finally page A is finally swapped out
5. now see the page A - it appears as if it was accessed (pte unmapped
so idle bit not set in output) - but it's incorrect.
To fix this, we store the idle information into a new idle bit of the
swap PTE during swapping of anonymous pages.
Also in the future, madvise extensions will allow a system process
manager (like Android's ActivityManager) to swap pages out of a process
that it knows will be cold. To an external process like a heap profiler
that is doing idle tracking on another process, this procedure will
interfere with the idle page tracking similar to the above steps.
Suggested-by: Minchan Kim <minc...@kernel.org>
Signed-off-by: Joel Fernandes (Google) <j...@joelfernandes.org>
---
arch/Kconfig | 3 +++
include/asm-generic/pgtable.h | 6 ++++++
mm/page_idle.c | 26 ++++++++++++++++++++++++--
mm/rmap.c | 2 ++
4 files changed, 35 insertions(+), 2 deletions(-)
diff --git a/arch/Kconfig b/arch/Kconfig
index a7b57dd42c26..3aa121ce824e 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -575,6 +575,9 @@ config ARCH_WANT_HUGE_PMD_SHARE
config HAVE_ARCH_SOFT_DIRTY
bool
+config HAVE_ARCH_PTE_SWP_PGIDLE
+ bool
+
config HAVE_MOD_ARCH_SPECIFIC
bool
help
diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
index 75d9d68a6de7..6d51d0a355a7 100644
--- a/include/asm-generic/pgtable.h
+++ b/include/asm-generic/pgtable.h
@@ -712,6 +712,12 @@ static inline void ptep_modify_prot_commit(struct
vm_area_struct *vma,
#define arch_start_context_switch(prev) do {} while (0)
#endif
+#ifndef CONFIG_HAVE_ARCH_PTE_SWP_PGIDLE
+static inline pte_t pte_swp_mkpage_idle(pte_t pte) { return pte; }
+static inline int pte_swp_page_idle(pte_t pte) { return 0; }
+static inline pte_t pte_swp_clear_mkpage_idle(pte_t pte) { return pte; }
+#endif
+
#ifdef CONFIG_HAVE_ARCH_SOFT_DIRTY
#ifndef CONFIG_ARCH_ENABLE_THP_MIGRATION
static inline pmd_t pmd_swp_mksoft_dirty(pmd_t pmd)
diff --git a/mm/page_idle.c b/mm/page_idle.c
index 9de4f4c67a8c..2766d4ab348c 100644
--- a/mm/page_idle.c
+++ b/mm/page_idle.c
@@ -276,7 +276,7 @@ struct page_idle_proc_priv {
};
/*
- * Add page to list to be set as idle later.
+ * Set a page as idle or add it to a list to be set as idle later.
*/
static void pte_page_idle_proc_add(struct page *page,
unsigned long addr, struct mm_walk *walk)
@@ -303,6 +303,13 @@ static void pte_page_idle_proc_add(struct page *page,
page_get = page_idle_get_page(page);
if (!page_get)
return;
+ } else {
+ /* For swapped pages, set output bit as idle */
+ frames = (addr - priv->start_addr) >> PAGE_SHIFT;
+ bit = frames % BITMAP_CHUNK_BITS;
+ chunk = &chunk[frames / BITMAP_CHUNK_BITS];
+ *chunk |= (1 << bit);
+ return;
}
/*
@@ -323,6 +330,7 @@ static int pte_page_idle_proc_range(pmd_t *pmd, unsigned
long addr,
spinlock_t *ptl;
struct page *page;
struct vm_area_struct *vma = walk->vma;
+ struct page_idle_proc_priv *priv = walk->private;
ptl = pmd_trans_huge_lock(pmd, vma);
if (ptl) {
@@ -341,6 +349,19 @@ static int pte_page_idle_proc_range(pmd_t *pmd, unsigned
long addr,
pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
for (; addr != end; pte++, addr += PAGE_SIZE) {
+ /* For swap_pte handling, we use an idle bit in the swap pte. */
+ if (is_swap_pte(*pte)) {
+ if (priv->write) {
+ set_pte_at(walk->mm, addr, pte,
+ pte_swp_mkpage_idle(*pte));
+ } else {
+ /* If swap pte has idle bit set, report it as
idle */
+ if (pte_swp_page_idle(*pte))
+ pte_page_idle_proc_add(NULL, addr,
walk);
+ }
+ continue;
+ }
+
if (!pte_present(*pte))
continue;
@@ -432,7 +453,8 @@ ssize_t page_idle_proc_generic(struct file *file, char
__user *ubuff,
set_page_idle(page);
}
} else {
- if (page_idle_pte_check(page)) {
+ /* If page is NULL, it was swapped out */
+ if (!page || page_idle_pte_check(page)) {
off = ((cur->addr) >> PAGE_SHIFT) - start_frame;
bit = off % BITMAP_CHUNK_BITS;
index = off / BITMAP_CHUNK_BITS;
diff --git a/mm/rmap.c b/mm/rmap.c
index e5dfe2ae6b0d..4bd618aab402 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1629,6 +1629,8 @@ static bool try_to_unmap_one(struct page *page, struct
vm_area_struct *vma,
swp_pte = swp_entry_to_pte(entry);
if (pte_soft_dirty(pteval))
swp_pte = pte_swp_mksoft_dirty(swp_pte);
+ if (page_is_idle(page))
+ swp_pte = pte_swp_mkpage_idle(swp_pte);
set_pte_at(mm, address, pvmw.pte, swp_pte);
/* Invalidate as we cleared the pte */
mmu_notifier_invalidate_range(mm, address,
--
2.22.0.770.g0f2c4a37fd-goog
