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SubjectRe: [RFC] high system time & lock contention running large mixed workload
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On Tue, 2009-12-01 at 21:23 +0900, KOSAKI Motohiro wrote:
> (cc to some related person)

>
> At first look,
>
> - We have to fix this issue certenally.
> - But your patch is a bit risky.
>
> Your patch treat trylock(pte-lock) failure as no accessced. but
> generally lock contention imply to have contention peer. iow, the page
> have reference bit typically. then, next shrink_inactive_list() move it
> active list again. that's suboptimal result.
>
> However, we can't treat lock-contention as page-is-referenced simply. if it does,
> the system easily go into OOM.
>
> So,
> if (priority < DEF_PRIORITY - 2)
> page_referenced()
> else
> page_refenced_trylock()
>
> is better?
> On typical workload, almost vmscan only use DEF_PRIORITY. then,
> if priority==DEF_PRIORITY situation don't cause heavy lock contention,
> the system don't need to mind the contention. anyway we can't avoid
> contention if the system have heavy memory pressure.
>


Agreed. The attached updated patch only does a trylock in the
page_referenced() call from shrink_inactive_list() and only for
anonymous pages when the priority is either 10, 11 or
12(DEF_PRIORITY-2). I have never seen a problem like this with active
pagecache pages and it does not alter the existing shrink_page_list
behavior. What do you think about this???




diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index cb0ba70..d7eaeca 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -80,7 +80,7 @@ static inline void page_dup_rmap(struct page *page)
* Called from mm/vmscan.c to handle paging out
*/
int page_referenced(struct page *, int is_locked,
- struct mem_cgroup *cnt, unsigned long *vm_flags);
+ struct mem_cgroup *cnt, unsigned long *vm_flags, int try);
enum ttu_flags {
TTU_UNMAP = 0, /* unmap mode */
TTU_MIGRATION = 1, /* migration mode */
@@ -99,7 +99,7 @@ int try_to_unmap(struct page *, enum ttu_flags flags);
* Called from mm/filemap_xip.c to unmap empty zero page
*/
pte_t *page_check_address(struct page *, struct mm_struct *,
- unsigned long, spinlock_t **, int);
+ unsigned long, spinlock_t **, int, int);

/*
* Used by swapoff to help locate where page is expected in vma.
@@ -135,7 +135,8 @@ int page_mapped_in_vma(struct page *page, struct vm_area_struct *vma);

static inline int page_referenced(struct page *page, int is_locked,
struct mem_cgroup *cnt,
- unsigned long *vm_flags)
+ unsigned long *vm_flags,
+ int try)
{
*vm_flags = 0;
return TestClearPageReferenced(page);
diff --git a/mm/filemap_xip.c b/mm/filemap_xip.c
index 1888b2d..35be29d 100644
--- a/mm/filemap_xip.c
+++ b/mm/filemap_xip.c
@@ -188,7 +188,7 @@ retry:
address = vma->vm_start +
((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
BUG_ON(address < vma->vm_start || address >= vma->vm_end);
- pte = page_check_address(page, mm, address, &ptl, 1);
+ pte = page_check_address(page, mm, address, &ptl, 1, 0);
if (pte) {
/* Nuke the page table entry. */
flush_cache_page(vma, address, pte_pfn(*pte));
diff --git a/mm/ksm.c b/mm/ksm.c
index 5575f86..8abb14b 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -623,7 +623,7 @@ static int write_protect_page(struct vm_area_struct *vma, struct page *page,
if (addr == -EFAULT)
goto out;

- ptep = page_check_address(page, mm, addr, &ptl, 0);
+ ptep = page_check_address(page, mm, addr, &ptl, 0, 0);
if (!ptep)
goto out;

diff --git a/mm/rmap.c b/mm/rmap.c
index dd43373..d8afe1a 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -270,7 +270,7 @@ unsigned long page_address_in_vma(struct page *page, struct vm_area_struct *vma)
* On success returns with pte mapped and locked.
*/
pte_t *page_check_address(struct page *page, struct mm_struct *mm,
- unsigned long address, spinlock_t **ptlp, int sync)
+ unsigned long address, spinlock_t **ptlp, int sync, int try)
{
pgd_t *pgd;
pud_t *pud;
@@ -298,7 +298,13 @@ pte_t *page_check_address(struct page *page, struct mm_struct *mm,
}

ptl = pte_lockptr(mm, pmd);
- spin_lock(ptl);
+ if (try) {
+ if (!spin_trylock(ptl)) {
+ pte_unmap(pte);
+ return NULL;
+ }
+ } else
+ spin_lock(ptl);
if (pte_present(*pte) && page_to_pfn(page) == pte_pfn(*pte)) {
*ptlp = ptl;
return pte;
@@ -325,7 +331,7 @@ int page_mapped_in_vma(struct page *page, struct vm_area_struct *vma)
address = vma_address(page, vma);
if (address == -EFAULT) /* out of vma range */
return 0;
- pte = page_check_address(page, vma->vm_mm, address, &ptl, 1);
+ pte = page_check_address(page, vma->vm_mm, address, &ptl, 1, 0);
if (!pte) /* the page is not in this mm */
return 0;
pte_unmap_unlock(pte, ptl);
@@ -340,7 +346,8 @@ int page_mapped_in_vma(struct page *page, struct vm_area_struct *vma)
static int page_referenced_one(struct page *page,
struct vm_area_struct *vma,
unsigned int *mapcount,
- unsigned long *vm_flags)
+ unsigned long *vm_flags,
+ int try)
{
struct mm_struct *mm = vma->vm_mm;
unsigned long address;
@@ -352,7 +359,7 @@ static int page_referenced_one(struct page *page,
if (address == -EFAULT)
goto out;

- pte = page_check_address(page, mm, address, &ptl, 0);
+ pte = page_check_address(page, mm, address, &ptl, 0, try);
if (!pte)
goto out;

@@ -396,7 +403,8 @@ out:

static int page_referenced_anon(struct page *page,
struct mem_cgroup *mem_cont,
- unsigned long *vm_flags)
+ unsigned long *vm_flags,
+ int try)
{
unsigned int mapcount;
struct anon_vma *anon_vma;
@@ -417,7 +425,7 @@ static int page_referenced_anon(struct page *page,
if (mem_cont && !mm_match_cgroup(vma->vm_mm, mem_cont))
continue;
referenced += page_referenced_one(page, vma,
- &mapcount, vm_flags);
+ &mapcount, vm_flags, try);
if (!mapcount)
break;
}
@@ -482,7 +490,7 @@ static int page_referenced_file(struct page *page,
if (mem_cont && !mm_match_cgroup(vma->vm_mm, mem_cont))
continue;
referenced += page_referenced_one(page, vma,
- &mapcount, vm_flags);
+ &mapcount, vm_flags, 0);
if (!mapcount)
break;
}
@@ -504,7 +512,8 @@ static int page_referenced_file(struct page *page,
int page_referenced(struct page *page,
int is_locked,
struct mem_cgroup *mem_cont,
- unsigned long *vm_flags)
+ unsigned long *vm_flags,
+ int try)
{
int referenced = 0;

@@ -515,7 +524,7 @@ int page_referenced(struct page *page,
if (page_mapped(page) && page->mapping) {
if (PageAnon(page))
referenced += page_referenced_anon(page, mem_cont,
- vm_flags);
+ vm_flags, try);
else if (is_locked)
referenced += page_referenced_file(page, mem_cont,
vm_flags);
@@ -547,7 +556,7 @@ static int page_mkclean_one(struct page *page, struct vm_area_struct *vma)
if (address == -EFAULT)
goto out;

- pte = page_check_address(page, mm, address, &ptl, 1);
+ pte = page_check_address(page, mm, address, &ptl, 1, 0);
if (!pte)
goto out;

@@ -774,7 +783,7 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
if (address == -EFAULT)
goto out;

- pte = page_check_address(page, mm, address, &ptl, 0);
+ pte = page_check_address(page, mm, address, &ptl, 0, 0);
if (!pte)
goto out;

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 777af57..fff63a0 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -643,7 +643,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
}

referenced = page_referenced(page, 1,
- sc->mem_cgroup, &vm_flags);
+ sc->mem_cgroup, &vm_flags, 0);
/*
* In active use or really unfreeable? Activate it.
* If page which have PG_mlocked lost isoltation race,
@@ -1355,7 +1355,8 @@ static void shrink_active_list(unsigned long nr_pages, struct zone *zone,

/* page_referenced clears PageReferenced */
if (page_mapping_inuse(page) &&
- page_referenced(page, 0, sc->mem_cgroup, &vm_flags)) {
+ page_referenced(page, 0, sc->mem_cgroup, &vm_flags,
+ priority<DEF_PRIORITY-2?0:1)) {
nr_rotated++;
/*
* Identify referenced, file-backed active pages and
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