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Date: Mon, 13 Jun 2016 21:35:40 +0300
From: Ebru Akagunduz <ebru.akagunduz@...il.com>
To: linux-mm@...ck.org
Cc: hughd@...gle.com, riel@...hat.com, akpm@...ux-foundation.org,
kirill.shutemov@...ux.intel.com, n-horiguchi@...jp.nec.com,
aarcange@...hat.com, iamjoonsoo.kim@....com, gorcunov@...nvz.org,
linux-kernel@...r.kernel.org, mgorman@...e.de, rientjes@...gle.com,
vbabka@...e.cz, aneesh.kumar@...ux.vnet.ibm.com,
hannes@...xchg.org, mhocko@...e.cz, boaz@...xistor.com,
minchan@...nel.org
Subject: Re: [RFC PATCH 2/3] mm, thp: convert from optimistic to conservative
On Sat, Jun 11, 2016 at 10:16:00PM +0300, Ebru Akagunduz wrote:
> Currently, khugepaged collapses pages saying only
> a referenced page enough to create a THP.
>
> This patch changes the design from optimistic to conservative.
> It gives a default threshold which is half of HPAGE_PMD_NR
> for referenced pages, also introduces a new sysfs knob.
>
> Signed-off-by: Ebru Akagunduz <ebru.akagunduz@...il.com>
Suggested-by: Minchan Kim <minchan@...nel.org>
> ---
Cc'ed Minchan Kim.
> include/trace/events/huge_memory.h | 10 ++++----
> mm/khugepaged.c | 50 +++++++++++++++++++++++++++++---------
> 2 files changed, 44 insertions(+), 16 deletions(-)
>
> diff --git a/include/trace/events/huge_memory.h b/include/trace/events/huge_memory.h
> index 830d47d..5f14025 100644
> --- a/include/trace/events/huge_memory.h
> +++ b/include/trace/events/huge_memory.h
> @@ -13,7 +13,7 @@
> EM( SCAN_EXCEED_NONE_PTE, "exceed_none_pte") \
> EM( SCAN_PTE_NON_PRESENT, "pte_non_present") \
> EM( SCAN_PAGE_RO, "no_writable_page") \
> - EM( SCAN_NO_REFERENCED_PAGE, "no_referenced_page") \
> + EM( SCAN_LACK_REFERENCED_PAGE, "lack_referenced_page") \
> EM( SCAN_PAGE_NULL, "page_null") \
> EM( SCAN_SCAN_ABORT, "scan_aborted") \
> EM( SCAN_PAGE_COUNT, "not_suitable_page_count") \
> @@ -47,7 +47,7 @@ SCAN_STATUS
> TRACE_EVENT(mm_khugepaged_scan_pmd,
>
> TP_PROTO(struct mm_struct *mm, struct page *page, bool writable,
> - bool referenced, int none_or_zero, int status, int unmapped),
> + int referenced, int none_or_zero, int status, int unmapped),
>
> TP_ARGS(mm, page, writable, referenced, none_or_zero, status, unmapped),
>
> @@ -55,7 +55,7 @@ TRACE_EVENT(mm_khugepaged_scan_pmd,
> __field(struct mm_struct *, mm)
> __field(unsigned long, pfn)
> __field(bool, writable)
> - __field(bool, referenced)
> + __field(int, referenced)
> __field(int, none_or_zero)
> __field(int, status)
> __field(int, unmapped)
> @@ -108,14 +108,14 @@ TRACE_EVENT(mm_collapse_huge_page,
> TRACE_EVENT(mm_collapse_huge_page_isolate,
>
> TP_PROTO(struct page *page, int none_or_zero,
> - bool referenced, bool writable, int status),
> + int referenced, bool writable, int status),
>
> TP_ARGS(page, none_or_zero, referenced, writable, status),
>
> TP_STRUCT__entry(
> __field(unsigned long, pfn)
> __field(int, none_or_zero)
> - __field(bool, referenced)
> + __field(int, referenced)
> __field(bool, writable)
> __field(int, status)
> ),
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index e3d8da7..43fc41e 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -27,7 +27,7 @@ enum scan_result {
> SCAN_EXCEED_NONE_PTE,
> SCAN_PTE_NON_PRESENT,
> SCAN_PAGE_RO,
> - SCAN_NO_REFERENCED_PAGE,
> + SCAN_LACK_REFERENCED_PAGE,
> SCAN_PAGE_NULL,
> SCAN_SCAN_ABORT,
> SCAN_PAGE_COUNT,
> @@ -68,6 +68,7 @@ static DECLARE_WAIT_QUEUE_HEAD(khugepaged_wait);
> */
> static unsigned int khugepaged_max_ptes_none __read_mostly;
> static unsigned int khugepaged_max_ptes_swap __read_mostly;
> +static unsigned int khugepaged_min_ptes_young __read_mostly;
>
> static int khugepaged(void *none);
>
> @@ -282,6 +283,32 @@ static struct kobj_attribute khugepaged_max_ptes_swap_attr =
> __ATTR(max_ptes_swap, 0644, khugepaged_max_ptes_swap_show,
> khugepaged_max_ptes_swap_store);
>
> +static ssize_t khugepaged_min_ptes_young_show(struct kobject *kobj,
> + struct kobj_attribute *attr,
> + char *buf)
> +{
> + return sprintf(buf, "%u\n", khugepaged_min_ptes_young);
> +}
> +
> +static ssize_t khugepaged_min_ptes_young_store(struct kobject *kobj,
> + struct kobj_attribute *attr,
> + const char *buf, size_t count)
> +{
> + int err;
> + unsigned long min_ptes_young;
> + err = kstrtoul(buf, 10, &min_ptes_young);
> + if (err || min_ptes_young > HPAGE_PMD_NR-1)
> + return -EINVAL;
> +
> + khugepaged_min_ptes_young = min_ptes_young;
> +
> + return count;
> +}
> +
> +static struct kobj_attribute khugepaged_min_ptes_young_attr =
> + __ATTR(min_ptes_young, 0644, khugepaged_min_ptes_young_show,
> + khugepaged_min_ptes_young_store);
> +
> static struct attribute *khugepaged_attr[] = {
> &khugepaged_defrag_attr.attr,
> &khugepaged_max_ptes_none_attr.attr,
> @@ -291,6 +318,7 @@ static struct attribute *khugepaged_attr[] = {
> &scan_sleep_millisecs_attr.attr,
> &alloc_sleep_millisecs_attr.attr,
> &khugepaged_max_ptes_swap_attr.attr,
> + &khugepaged_min_ptes_young_attr.attr,
> NULL,
> };
>
> @@ -502,8 +530,8 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
> {
> struct page *page = NULL;
> pte_t *_pte;
> - int none_or_zero = 0, result = 0;
> - bool referenced = false, writable = false;
> + int none_or_zero = 0, result = 0, referenced = 0;
> + bool writable = false;
>
> for (_pte = pte; _pte < pte+HPAGE_PMD_NR;
> _pte++, address += PAGE_SIZE) {
> @@ -582,14 +610,14 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
> VM_BUG_ON_PAGE(!PageLocked(page), page);
> VM_BUG_ON_PAGE(PageLRU(page), page);
>
> - /* If there is no mapped pte young don't collapse the page */
> + /* There should be enough young pte to collapse the page */
> if (pte_young(pteval) ||
> page_is_young(page) || PageReferenced(page) ||
> mmu_notifier_test_young(vma->vm_mm, address))
> - referenced = true;
> + referenced++;
> }
> if (likely(writable)) {
> - if (likely(referenced)) {
> + if (referenced >= khugepaged_min_ptes_young) {
> result = SCAN_SUCCEED;
> trace_mm_collapse_huge_page_isolate(page, none_or_zero,
> referenced, writable, result);
> @@ -1082,11 +1110,11 @@ static int khugepaged_scan_pmd(struct mm_struct *mm,
> pmd_t *pmd;
> pte_t *pte, *_pte;
> int ret = 0, none_or_zero = 0, result = 0;
> + int node = NUMA_NO_NODE, unmapped = 0, referenced = 0;
> struct page *page = NULL;
> unsigned long _address;
> spinlock_t *ptl;
> - int node = NUMA_NO_NODE, unmapped = 0;
> - bool writable = false, referenced = false;
> + bool writable = false;
>
> VM_BUG_ON(address & ~HPAGE_PMD_MASK);
>
> @@ -1174,14 +1202,14 @@ static int khugepaged_scan_pmd(struct mm_struct *mm,
> if (pte_young(pteval) ||
> page_is_young(page) || PageReferenced(page) ||
> mmu_notifier_test_young(vma->vm_mm, address))
> - referenced = true;
> + referenced++;
> }
> if (writable) {
> - if (referenced) {
> + if (referenced >= khugepaged_min_ptes_young) {
> result = SCAN_SUCCEED;
> ret = 1;
> } else {
> - result = SCAN_NO_REFERENCED_PAGE;
> + result = SCAN_LACK_REFERENCED_PAGE;
> }
> } else {
> result = SCAN_PAGE_RO;
> --
> 1.9.1
>
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