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Subject[RESEND RFC v4 1/3] mm: add tracepoint for scanning pages
Date
Using static tracepoints, data of functions is recorded.
It is good to automatize debugging without doing a lot
of changes in the source code.

This patch adds tracepoint for khugepaged_scan_pmd,
collapse_huge_page and __collapse_huge_page_isolate.

Signed-off-by: Ebru Akagunduz <ebru.akagunduz@gmail.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: Rik van Riel <riel@redhat.com>
---
Changes in v2:
- Nothing changed

Changes in v3:
- Print page address instead of vm_start (Vlastimil Babka)
- Define constants to specify exact tracepoint result (Vlastimil Babka)

Changes in v4:
- Change the constant prefix with SCAN_ instead of MM_ (Vlastimil Babka)
- Move the constants into the enum (Vlastimil Babka)
- Move the constants from mm.h to huge_memory.c
(because only will be used in huge_memory.c) (Vlastimil Babka)
- Print pfn in tracepoints (Vlastimil Babka)
- Print scan result as string in tracepoint (Vlastimil Babka)
(I tried to make same things to print string like mm/compaction.c.
My patch does not print string, I skip something but could not see why)

- Do not change function return values for success and failure,
leave them original agreed with Doc/CodingStyle (Vlastimil Babka)
- Define scan_result to specify tracepoint result (Ebru Akagunduz)
- Add out_nolock label to avoid multiple tracepoints (Vlastimil Babka)

include/trace/events/huge_memory.h | 100 ++++++++++++++++++++
mm/huge_memory.c | 187 +++++++++++++++++++++++++++++++------
2 files changed, 256 insertions(+), 31 deletions(-)
create mode 100644 include/trace/events/huge_memory.h

diff --git a/include/trace/events/huge_memory.h b/include/trace/events/huge_memory.h
new file mode 100644
index 0000000..36162a9
--- /dev/null
+++ b/include/trace/events/huge_memory.h
@@ -0,0 +1,100 @@
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM huge_memory
+
+#if !defined(__HUGE_MEMORY_H) || defined(TRACE_HEADER_MULTI_READ)
+#define __HUGE_MEMORY_H
+
+#include <linux/tracepoint.h>
+
+TRACE_EVENT(mm_khugepaged_scan_pmd,
+
+ TP_PROTO(struct mm_struct *mm, unsigned long pfn, bool writable,
+ bool referenced, int none_or_zero, int status),
+
+ TP_ARGS(mm, pfn, writable, referenced, none_or_zero, status),
+
+ TP_STRUCT__entry(
+ __field(struct mm_struct *, mm)
+ __field(unsigned long, pfn)
+ __field(bool, writable)
+ __field(bool, referenced)
+ __field(int, none_or_zero)
+ __field(int, status)
+ ),
+
+ TP_fast_assign(
+ __entry->mm = mm;
+ __entry->pfn = pfn;
+ __entry->writable = writable;
+ __entry->referenced = referenced;
+ __entry->none_or_zero = none_or_zero;
+ __entry->status = status;
+ ),
+
+ TP_printk("mm=%p, scan_pfn=0x%lx, writable=%d, referenced=%d, none_or_zero=%d, status=%s",
+ __entry->mm,
+ __entry->pfn,
+ __entry->writable,
+ __entry->referenced,
+ __entry->none_or_zero,
+ khugepaged_status_string[__entry->status])
+);
+
+TRACE_EVENT(mm_collapse_huge_page,
+
+ TP_PROTO(struct mm_struct *mm, int isolated, int status),
+
+ TP_ARGS(mm, isolated, status),
+
+ TP_STRUCT__entry(
+ __field(struct mm_struct *, mm)
+ __field(int, isolated)
+ __field(int, status)
+ ),
+
+ TP_fast_assign(
+ __entry->mm = mm;
+ __entry->isolated = isolated;
+ __entry->status = status;
+ ),
+
+ TP_printk("mm=%p, isolated=%d, status=%s",
+ __entry->mm,
+ __entry->isolated,
+ khugepaged_status_string[__entry->status])
+);
+
+TRACE_EVENT(mm_collapse_huge_page_isolate,
+
+ TP_PROTO(unsigned long pfn, int none_or_zero,
+ bool referenced, bool writable, int status),
+
+ TP_ARGS(pfn, none_or_zero, referenced, writable, status),
+
+ TP_STRUCT__entry(
+ __field(unsigned long, pfn)
+ __field(int, none_or_zero)
+ __field(bool, referenced)
+ __field(bool, writable)
+ __field(int, status)
+ ),
+
+ TP_fast_assign(
+ __entry->pfn = pfn;
+ __entry->none_or_zero = none_or_zero;
+ __entry->referenced = referenced;
+ __entry->writable = writable;
+ __entry->status = status;
+ ),
+
+ TP_printk("scan_pfn=0x%lx, none_or_zero=%d, referenced=%d, writable=%d, status=%s",
+ __entry->pfn,
+ __entry->none_or_zero,
+ __entry->referenced,
+ __entry->writable,
+ khugepaged_status_string[__entry->status])
+);
+
+#endif /* __HUGE_MEMORY_H */
+#include <trace/define_trace.h>
+
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 097c7a4..71a7c43 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -28,6 +28,57 @@
#include <asm/pgalloc.h>
#include "internal.h"

+static const char *const khugepaged_status_string[] = {
+ "failed",
+ "succeeded",
+ "pmd_null",
+ "exceeded_none_pte",
+ "non-present_pte",
+ "no_writable_page",
+ "no_referenced_page",
+ "page_null",
+ "scan_aborted",
+ "not_suitable_page_count",
+ "page_not_in_lru",
+ "page_locked",
+ "page_not_anon",
+ "no_process_for_page",
+ "vma_null",
+ "vma_check_fail",
+ "not_suitable_address_range",
+ "page_swap_cache",
+ "could_not_delete_page_from_lru",
+ "alloc_huge_page_fail",
+ "ccgroup_charge_fail"
+};
+
+enum scan_result {
+ SCAN_OPERATION_FAIL,
+ SCAN_OPERATION_SUCCEED,
+ SCAN_PMD_NULL,
+ SCAN_EXCEED_NONE_PTE,
+ SCAN_PTE_NON_PRESENT,
+ SCAN_PAGE_RO,
+ SCAN_NO_REFERENCED_PAGE,
+ SCAN_PAGE_NULL,
+ SCAN_SCAN_ABORT,
+ SCAN_PAGE_COUNT,
+ SCAN_PAGE_LRU,
+ SCAN_PAGE_LOCK,
+ SCAN_PAGE_ANON,
+ SCAN_ANY_PROCESS,
+ SCAN_VMA_NULL,
+ SCAN_VMA_CHECK,
+ SCAN_ADDRESS_RANGE,
+ SCAN_SWAP_CACHE_PAGE,
+ SCAN_DEL_PAGE_LRU,
+ SCAN_ALLOC_HUGE_PAGE_FAIL,
+ SCAN_CGROUP_CHARGE_FAIL
+};
+
+#define CREATE_TRACE_POINTS
+#include <trace/events/huge_memory.h>
+
/*
* By default transparent hugepage support is disabled in order that avoid
* to risk increase the memory footprint of applications without a guaranteed
@@ -2125,24 +2176,30 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
unsigned long address,
pte_t *pte)
{
- struct page *page;
+ struct page *page = NULL;
pte_t *_pte;
- int none_or_zero = 0;
+ int none_or_zero = 0, result = 0;
bool referenced = false, writable = false;
for (_pte = pte; _pte < pte+HPAGE_PMD_NR;
_pte++, address += PAGE_SIZE) {
pte_t pteval = *_pte;
if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
- if (++none_or_zero <= khugepaged_max_ptes_none)
+ if (++none_or_zero <= khugepaged_max_ptes_none) {
continue;
- else
+ } else {
+ result = SCAN_EXCEED_NONE_PTE;
goto out;
+ }
}
- if (!pte_present(pteval))
+ if (!pte_present(pteval)) {
+ result = SCAN_PTE_NON_PRESENT;
goto out;
+ }
page = vm_normal_page(vma, address, pteval);
- if (unlikely(!page))
+ if (unlikely(!page)) {
+ result = SCAN_PAGE_NULL;
goto out;
+ }

VM_BUG_ON_PAGE(PageCompound(page), page);
VM_BUG_ON_PAGE(!PageAnon(page), page);
@@ -2154,8 +2211,10 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
* is needed to serialize against split_huge_page
* when invoked from the VM.
*/
- if (!trylock_page(page))
+ if (!trylock_page(page)) {
+ result = SCAN_PAGE_LOCK;
goto out;
+ }

/*
* cannot use mapcount: can't collapse if there's a gup pin.
@@ -2164,6 +2223,7 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
*/
if (page_count(page) != 1 + !!PageSwapCache(page)) {
unlock_page(page);
+ result = SCAN_PAGE_COUNT;
goto out;
}
if (pte_write(pteval)) {
@@ -2171,6 +2231,7 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
} else {
if (PageSwapCache(page) && !reuse_swap_page(page)) {
unlock_page(page);
+ result = SCAN_SWAP_CACHE_PAGE;
goto out;
}
/*
@@ -2185,6 +2246,7 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
*/
if (isolate_lru_page(page)) {
unlock_page(page);
+ result = SCAN_DEL_PAGE_LRU;
goto out;
}
/* 0 stands for page_is_file_cache(page) == false */
@@ -2197,10 +2259,21 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
mmu_notifier_test_young(vma->vm_mm, address))
referenced = true;
}
- if (likely(referenced && writable))
- return 1;
+ if (likely(writable)) {
+ if (likely(referenced)) {
+ result = SCAN_OPERATION_SUCCEED;
+ trace_mm_collapse_huge_page_isolate(page_to_pfn(page), none_or_zero,
+ referenced, writable, result);
+ return 1;
+ }
+ } else {
+ result = SCAN_PAGE_RO;
+ }
+
out:
release_pte_pages(pte, _pte);
+ trace_mm_collapse_huge_page_isolate(page_to_pfn(page), none_or_zero,
+ referenced, writable, result);
return 0;
}

@@ -2435,7 +2508,7 @@ static void collapse_huge_page(struct mm_struct *mm,
pgtable_t pgtable;
struct page *new_page;
spinlock_t *pmd_ptl, *pte_ptl;
- int isolated;
+ int isolated, result = 0;
unsigned long hstart, hend;
struct mem_cgroup *memcg;
unsigned long mmun_start; /* For mmu_notifiers */
@@ -2450,12 +2523,16 @@ static void collapse_huge_page(struct mm_struct *mm,

/* release the mmap_sem read lock. */
new_page = khugepaged_alloc_page(hpage, gfp, mm, vma, address, node);
- if (!new_page)
- return;
+ if (!new_page) {
+ result = SCAN_ALLOC_HUGE_PAGE_FAIL;
+ goto out_nolock;
+ }

if (unlikely(mem_cgroup_try_charge(new_page, mm,
- gfp, &memcg)))
- return;
+ gfp, &memcg))) {
+ result = SCAN_CGROUP_CHARGE_FAIL;
+ goto out_nolock;
+ }

/*
* Prevent all access to pagetables with the exception of
@@ -2463,21 +2540,31 @@ static void collapse_huge_page(struct mm_struct *mm,
* handled by the anon_vma lock + PG_lock.
*/
down_write(&mm->mmap_sem);
- if (unlikely(khugepaged_test_exit(mm)))
+ if (unlikely(khugepaged_test_exit(mm))) {
+ result = SCAN_ANY_PROCESS;
goto out;
+ }

vma = find_vma(mm, address);
- if (!vma)
+ if (!vma) {
+ result = SCAN_VMA_NULL;
goto out;
+ }
hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
hend = vma->vm_end & HPAGE_PMD_MASK;
- if (address < hstart || address + HPAGE_PMD_SIZE > hend)
+ if (address < hstart || address + HPAGE_PMD_SIZE > hend) {
+ result = SCAN_ADDRESS_RANGE;
goto out;
- if (!hugepage_vma_check(vma))
+ }
+ if (!hugepage_vma_check(vma)) {
+ result = SCAN_VMA_CHECK;
goto out;
+ }
pmd = mm_find_pmd(mm, address);
- if (!pmd)
+ if (!pmd) {
+ result = SCAN_PMD_NULL;
goto out;
+ }

anon_vma_lock_write(vma->anon_vma);

@@ -2514,6 +2601,7 @@ static void collapse_huge_page(struct mm_struct *mm,
pmd_populate(mm, pmd, pmd_pgtable(_pmd));
spin_unlock(pmd_ptl);
anon_vma_unlock_write(vma->anon_vma);
+ result = SCAN_OPERATION_FAIL;
goto out;
}

@@ -2551,10 +2639,15 @@ static void collapse_huge_page(struct mm_struct *mm,
*hpage = NULL;

khugepaged_pages_collapsed++;
+ result = SCAN_OPERATION_SUCCEED;
out_up_write:
up_write(&mm->mmap_sem);
+ trace_mm_collapse_huge_page(mm, isolated, result);
return;

+out_nolock:
+ trace_mm_collapse_huge_page(mm, isolated, result);
+ return;
out:
mem_cgroup_cancel_charge(new_page, memcg);
goto out_up_write;
@@ -2567,8 +2660,8 @@ static int khugepaged_scan_pmd(struct mm_struct *mm,
{
pmd_t *pmd;
pte_t *pte, *_pte;
- int ret = 0, none_or_zero = 0;
- struct page *page;
+ int ret = 0, none_or_zero = 0, result = 0;
+ struct page *page = NULL;
unsigned long _address;
spinlock_t *ptl;
int node = NUMA_NO_NODE;
@@ -2577,8 +2670,10 @@ static int khugepaged_scan_pmd(struct mm_struct *mm,
VM_BUG_ON(address & ~HPAGE_PMD_MASK);

pmd = mm_find_pmd(mm, address);
- if (!pmd)
+ if (!pmd) {
+ result = SCAN_PMD_NULL;
goto out;
+ }

memset(khugepaged_node_load, 0, sizeof(khugepaged_node_load));
pte = pte_offset_map_lock(mm, pmd, address, &ptl);
@@ -2586,19 +2681,25 @@ static int khugepaged_scan_pmd(struct mm_struct *mm,
_pte++, _address += PAGE_SIZE) {
pte_t pteval = *_pte;
if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
- if (++none_or_zero <= khugepaged_max_ptes_none)
+ if (++none_or_zero <= khugepaged_max_ptes_none) {
continue;
- else
+ } else {
+ result = SCAN_EXCEED_NONE_PTE;
goto out_unmap;
+ }
}
- if (!pte_present(pteval))
+ if (!pte_present(pteval)) {
+ result = SCAN_PTE_NON_PRESENT;
goto out_unmap;
+ }
if (pte_write(pteval))
writable = true;

page = vm_normal_page(vma, _address, pteval);
- if (unlikely(!page))
+ if (unlikely(!page)) {
+ result = SCAN_PAGE_NULL;
goto out_unmap;
+ }
/*
* Record which node the original page is from and save this
* information to khugepaged_node_load[].
@@ -2606,25 +2707,47 @@ static int khugepaged_scan_pmd(struct mm_struct *mm,
* hit record.
*/
node = page_to_nid(page);
- if (khugepaged_scan_abort(node))
+ if (khugepaged_scan_abort(node)) {
+ result = SCAN_SCAN_ABORT;
goto out_unmap;
+ }
khugepaged_node_load[node]++;
VM_BUG_ON_PAGE(PageCompound(page), page);
- if (!PageLRU(page) || PageLocked(page) || !PageAnon(page))
+ if (!PageLRU(page)) {
+ result = SCAN_SCAN_ABORT;
goto out_unmap;
+ }
+ if (PageLocked(page)) {
+ result = SCAN_PAGE_LOCK;
+ goto out_unmap;
+ }
+ if (!PageAnon(page)) {
+ result = SCAN_PAGE_ANON;
+ goto out_unmap;
+ }
/*
* cannot use mapcount: can't collapse if there's a gup pin.
* The page must only be referenced by the scanned process
* and page swap cache.
*/
- if (page_count(page) != 1 + !!PageSwapCache(page))
+ if (page_count(page) != 1 + !!PageSwapCache(page)) {
+ result = SCAN_PAGE_COUNT;
goto out_unmap;
+ }
if (pte_young(pteval) || PageReferenced(page) ||
mmu_notifier_test_young(vma->vm_mm, address))
referenced = true;
}
- if (referenced && writable)
- ret = 1;
+ if (writable) {
+ if (referenced) {
+ result = SCAN_OPERATION_SUCCEED;
+ ret = 1;
+ } else {
+ result = SCAN_NO_REFERENCED_PAGE;
+ }
+ } else {
+ result = SCAN_PAGE_RO;
+ }
out_unmap:
pte_unmap_unlock(pte, ptl);
if (ret) {
@@ -2633,6 +2756,8 @@ out_unmap:
collapse_huge_page(mm, address, hpage, vma, node);
}
out:
+ trace_mm_khugepaged_scan_pmd(mm, page_to_pfn(page), writable, referenced,
+ none_or_zero, result);
return ret;
}

--
1.9.1


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