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khugepaged: introduce 'max_ptes_shared' tunable

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'max_ptes_shared' specifies how many pages can be shared across multiple
processes.  Exceeding the number would block the collapse::

	/sys/kernel/mm/transparent_hugepage/khugepaged/max_ptes_shared

A higher value may increase memory footprint for some workloads.

By default, at least half of pages has to be not shared.

[colin.king@canonical.com: fix several spelling mistakes]
  Link: http://lkml.kernel.org/r/20200420084241.65433-1-colin.king@canonical.com
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Tested-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Acked-by: Yang Shi <yang.shi@linux.alibaba.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Link: http://lkml.kernel.org/r/20200416160026.16538-9-kirill.shutemov@linux.intel.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Kirill A. Shutemov 2020-06-03 16:00:30 -07:00 committed by Linus Torvalds
parent 3917c80280
commit 71a2c112a0
4 changed files with 140 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
Documentation/admin-guide/mm/transhuge.rst
View File

@ -220,6 +220,13 @@ memory. A lower value can prevent THPs from being
collapsed, resulting fewer pages being collapsed into
THPs, and lower memory access performance.
``max_ptes_shared`` specifies how many pages can be shared across multiple
processes. Exceeding the number would block the collapse::
/sys/kernel/mm/transparent_hugepage/khugepaged/max_ptes_shared
A higher value may increase memory footprint for some workloads.
Boot parameter
==============

3
include/trace/events/huge_memory.h
View File

@ -12,6 +12,8 @@
EM( SCAN_SUCCEED, "succeeded") \
EM( SCAN_PMD_NULL, "pmd_null") \
EM( SCAN_EXCEED_NONE_PTE, "exceed_none_pte") \
EM( SCAN_EXCEED_SWAP_PTE, "exceed_swap_pte") \
EM( SCAN_EXCEED_SHARED_PTE, "exceed_shared_pte") \
EM( SCAN_PTE_NON_PRESENT, "pte_non_present") \
EM( SCAN_PTE_UFFD_WP, "pte_uffd_wp") \
EM( SCAN_PAGE_RO, "no_writable_page") \
@ -31,7 +33,6 @@
EM( SCAN_DEL_PAGE_LRU, "could_not_delete_page_from_lru")\
EM( SCAN_ALLOC_HUGE_PAGE_FAIL, "alloc_huge_page_failed") \
EM( SCAN_CGROUP_CHARGE_FAIL, "ccgroup_charge_failed") \
EM( SCAN_EXCEED_SWAP_PTE, "exceed_swap_pte") \
EM( SCAN_TRUNCATED, "truncated") \
EMe(SCAN_PAGE_HAS_PRIVATE, "page_has_private") \

52
mm/khugepaged.c
View File

@ -28,6 +28,8 @@ enum scan_result {
SCAN_SUCCEED,
SCAN_PMD_NULL,
SCAN_EXCEED_NONE_PTE,
SCAN_EXCEED_SWAP_PTE,
SCAN_EXCEED_SHARED_PTE,
SCAN_PTE_NON_PRESENT,
SCAN_PTE_UFFD_WP,
SCAN_PAGE_RO,
@ -47,7 +49,6 @@ enum scan_result {
SCAN_DEL_PAGE_LRU,
SCAN_ALLOC_HUGE_PAGE_FAIL,
SCAN_CGROUP_CHARGE_FAIL,
SCAN_EXCEED_SWAP_PTE,
SCAN_TRUNCATED,
SCAN_PAGE_HAS_PRIVATE,
};
@ -72,6 +73,7 @@ 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_max_ptes_shared __read_mostly;
#define MM_SLOTS_HASH_BITS 10
static __read_mostly DEFINE_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS);
@ -291,15 +293,43 @@ 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_max_ptes_shared_show(struct kobject *kobj,
struct kobj_attribute *attr,
char *buf)
{
return sprintf(buf, "%u\n", khugepaged_max_ptes_shared);
}
static ssize_t khugepaged_max_ptes_shared_store(struct kobject *kobj,
struct kobj_attribute *attr,
const char *buf, size_t count)
{
int err;
unsigned long max_ptes_shared;
err = kstrtoul(buf, 10, &max_ptes_shared);
if (err || max_ptes_shared > HPAGE_PMD_NR-1)
return -EINVAL;
khugepaged_max_ptes_shared = max_ptes_shared;
return count;
}
static struct kobj_attribute khugepaged_max_ptes_shared_attr =
__ATTR(max_ptes_shared, 0644, khugepaged_max_ptes_shared_show,
khugepaged_max_ptes_shared_store);
static struct attribute *khugepaged_attr[] = {
&khugepaged_defrag_attr.attr,
&khugepaged_max_ptes_none_attr.attr,
&khugepaged_max_ptes_swap_attr.attr,
&khugepaged_max_ptes_shared_attr.attr,
&pages_to_scan_attr.attr,
&pages_collapsed_attr.attr,
&full_scans_attr.attr,
&scan_sleep_millisecs_attr.attr,
&alloc_sleep_millisecs_attr.attr,
&khugepaged_max_ptes_swap_attr.attr,
NULL,
};
@ -359,6 +389,7 @@ int __init khugepaged_init(void)
khugepaged_pages_to_scan = HPAGE_PMD_NR * 8;
khugepaged_max_ptes_none = HPAGE_PMD_NR - 1;
khugepaged_max_ptes_swap = HPAGE_PMD_NR / 8;
khugepaged_max_ptes_shared = HPAGE_PMD_NR / 2;
return 0;
}
@ -557,7 +588,7 @@ 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, referenced = 0;
int none_or_zero = 0, shared = 0, result = 0, referenced = 0;
bool writable = false;
for (_pte = pte; _pte < pte+HPAGE_PMD_NR;
@ -585,6 +616,12 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
VM_BUG_ON_PAGE(!PageAnon(page), page);
if (page_mapcount(page) > 1 &&
++shared > khugepaged_max_ptes_shared) {
result = SCAN_EXCEED_SHARED_PTE;
goto out;
}
if (PageCompound(page)) {
struct page *p;
page = compound_head(page);
@ -1168,7 +1205,8 @@ 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, referenced = 0;
int ret = 0, result = 0, referenced = 0;
int none_or_zero = 0, shared = 0;
struct page *page = NULL;
unsigned long _address;
spinlock_t *ptl;
@ -1240,6 +1278,12 @@ static int khugepaged_scan_pmd(struct mm_struct *mm,
goto out_unmap;
}
if (page_mapcount(page) > 1 &&
++shared > khugepaged_max_ptes_shared) {
result = SCAN_EXCEED_SHARED_PTE;
goto out_unmap;
}
page = compound_head(page);
/*

83
tools/testing/selftests/vm/khugepaged.c
View File

@ -78,6 +78,7 @@ struct khugepaged_settings {
unsigned int scan_sleep_millisecs;
unsigned int max_ptes_none;
unsigned int max_ptes_swap;
unsigned int max_ptes_shared;
unsigned long pages_to_scan;
};
@ -277,6 +278,7 @@ static void write_settings(struct settings *settings)
khugepaged->scan_sleep_millisecs);
write_num("khugepaged/max_ptes_none", khugepaged->max_ptes_none);
write_num("khugepaged/max_ptes_swap", khugepaged->max_ptes_swap);
write_num("khugepaged/max_ptes_shared", khugepaged->max_ptes_shared);
write_num("khugepaged/pages_to_scan", khugepaged->pages_to_scan);
}
@ -313,6 +315,7 @@ static void save_settings(void)
read_num("khugepaged/scan_sleep_millisecs"),
.max_ptes_none = read_num("khugepaged/max_ptes_none"),
.max_ptes_swap = read_num("khugepaged/max_ptes_swap"),
.max_ptes_shared = read_num("khugepaged/max_ptes_shared"),
.pages_to_scan = read_num("khugepaged/pages_to_scan"),
};
success("OK");
@ -896,12 +899,90 @@ static void collapse_fork_compound(void)
fail("Fail");
fill_memory(p, 0, page_size);
write_num("khugepaged/max_ptes_shared", hpage_pmd_nr - 1);
if (wait_for_scan("Collapse PTE table full of compound pages in child", p))
fail("Timeout");
else if (check_huge(p))
success("OK");
else
fail("Fail");
write_num("khugepaged/max_ptes_shared",
default_settings.khugepaged.max_ptes_shared);
validate_memory(p, 0, hpage_pmd_size);
munmap(p, hpage_pmd_size);
exit(exit_status);
}
wait(&wstatus);
exit_status += WEXITSTATUS(wstatus);
printf("Check if parent still has huge page...");
if (check_huge(p))
success("OK");
else
fail("Fail");
validate_memory(p, 0, hpage_pmd_size);
munmap(p, hpage_pmd_size);
}
static void collapse_max_ptes_shared()
{
int max_ptes_shared = read_num("khugepaged/max_ptes_shared");
int wstatus;
void *p;
p = alloc_mapping();
printf("Allocate huge page...");
madvise(p, hpage_pmd_size, MADV_HUGEPAGE);
fill_memory(p, 0, hpage_pmd_size);
if (check_huge(p))
success("OK");
else
fail("Fail");
printf("Share huge page over fork()...");
if (!fork()) {
/* Do not touch settings on child exit */
skip_settings_restore = true;
exit_status = 0;
if (check_huge(p))
success("OK");
else
fail("Fail");
printf("Trigger CoW on page %d of %d...",
hpage_pmd_nr - max_ptes_shared - 1, hpage_pmd_nr);
fill_memory(p, 0, (hpage_pmd_nr - max_ptes_shared - 1) * page_size);
if (!check_huge(p))
success("OK");
else
fail("Fail");
if (wait_for_scan("Do not collapse with max_ptes_shared exceeded", p))
fail("Timeout");
else if (!check_huge(p))
success("OK");
else
fail("Fail");
printf("Trigger CoW on page %d of %d...",
hpage_pmd_nr - max_ptes_shared, hpage_pmd_nr);
fill_memory(p, 0, (hpage_pmd_nr - max_ptes_shared) * page_size);
if (!check_huge(p))
success("OK");
else
fail("Fail");
if (wait_for_scan("Collapse with max_ptes_shared PTEs shared", p))
fail("Timeout");
else if (check_huge(p))
success("OK");
else
fail("Fail");
validate_memory(p, 0, hpage_pmd_size);
munmap(p, hpage_pmd_size);
@ -930,6 +1011,7 @@ int main(void)
default_settings.khugepaged.max_ptes_none = hpage_pmd_nr - 1;
default_settings.khugepaged.max_ptes_swap = hpage_pmd_nr / 8;
default_settings.khugepaged.max_ptes_shared = hpage_pmd_nr / 2;
default_settings.khugepaged.pages_to_scan = hpage_pmd_nr * 8;
save_settings();
@ -947,6 +1029,7 @@ int main(void)
collapse_compound_extreme();
collapse_fork();
collapse_fork_compound();
collapse_max_ptes_shared();
restore_settings(0);
}