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authorKirill A. Shutemov <kirill.shutemov@linux.intel.com>2016-01-15 16:53:42 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2016-01-15 17:56:32 -0800
commit53f9263baba69fc1630e3c780c4d11b72643f962 (patch)
tree7b8c3434d11c5cb6b58ea2463779d86cbff57d5e /mm/rmap.c
parent4b471e8898c3d0f5c97a3c73ac32d0549fe01c87 (diff)
downloadlinux-53f9263baba69fc1630e3c780c4d11b72643f962.tar.bz2
mm: rework mapcount accounting to enable 4k mapping of THPs
We're going to allow mapping of individual 4k pages of THP compound. It means we need to track mapcount on per small page basis. Straight-forward approach is to use ->_mapcount in all subpages to track how many time this subpage is mapped with PMDs or PTEs combined. But this is rather expensive: mapping or unmapping of a THP page with PMD would require HPAGE_PMD_NR atomic operations instead of single we have now. The idea is to store separately how many times the page was mapped as whole -- compound_mapcount. This frees up ->_mapcount in subpages to track PTE mapcount. We use the same approach as with compound page destructor and compound order to store compound_mapcount: use space in first tail page, ->mapping this time. Any time we map/unmap whole compound page (THP or hugetlb) -- we increment/decrement compound_mapcount. When we map part of compound page with PTE we operate on ->_mapcount of the subpage. page_mapcount() counts both: PTE and PMD mappings of the page. Basically, we have mapcount for a subpage spread over two counters. It makes tricky to detect when last mapcount for a page goes away. We introduced PageDoubleMap() for this. When we split THP PMD for the first time and there's other PMD mapping left we offset up ->_mapcount in all subpages by one and set PG_double_map on the compound page. These additional references go away with last compound_mapcount. This approach provides a way to detect when last mapcount goes away on per small page basis without introducing new overhead for most common cases. [akpm@linux-foundation.org: fix typo in comment] [mhocko@suse.com: ignore partial THP when moving task] Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Tested-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com> Acked-by: Jerome Marchand <jmarchan@redhat.com> Cc: Sasha Levin <sasha.levin@oracle.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com> Cc: Jerome Marchand <jmarchan@redhat.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: Dave Hansen <dave.hansen@intel.com> Cc: Mel Gorman <mgorman@suse.de> Cc: Rik van Riel <riel@redhat.com> Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> Cc: Steve Capper <steve.capper@linaro.org> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Christoph Lameter <cl@linux.com> Cc: David Rientjes <rientjes@google.com> Signed-off-by: Michal Hocko <mhocko@suse.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/rmap.c')
-rw-r--r--mm/rmap.c98
1 files changed, 76 insertions, 22 deletions
diff --git a/mm/rmap.c b/mm/rmap.c
index aa68a4089a53..2e6257165527 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1122,7 +1122,7 @@ static void __page_check_anon_rmap(struct page *page,
* over the call to page_add_new_anon_rmap.
*/
BUG_ON(page_anon_vma(page)->root != vma->anon_vma->root);
- BUG_ON(page->index != linear_page_index(vma, address));
+ BUG_ON(page_to_pgoff(page) != linear_page_index(vma, address));
#endif
}
@@ -1152,9 +1152,28 @@ void page_add_anon_rmap(struct page *page,
void do_page_add_anon_rmap(struct page *page,
struct vm_area_struct *vma, unsigned long address, int flags)
{
- int first = atomic_inc_and_test(&page->_mapcount);
+ bool compound = flags & RMAP_COMPOUND;
+ bool first;
+
+ if (PageTransCompound(page)) {
+ VM_BUG_ON_PAGE(!PageLocked(page), page);
+ if (compound) {
+ atomic_t *mapcount;
+
+ VM_BUG_ON_PAGE(!PageTransHuge(page), page);
+ mapcount = compound_mapcount_ptr(page);
+ first = atomic_inc_and_test(mapcount);
+ } else {
+ /* Anon THP always mapped first with PMD */
+ first = 0;
+ VM_BUG_ON_PAGE(!page_mapcount(page), page);
+ atomic_inc(&page->_mapcount);
+ }
+ } else {
+ first = atomic_inc_and_test(&page->_mapcount);
+ }
+
if (first) {
- bool compound = flags & RMAP_COMPOUND;
int nr = compound ? hpage_nr_pages(page) : 1;
/*
* We use the irq-unsafe __{inc|mod}_zone_page_stat because
@@ -1173,6 +1192,7 @@ void do_page_add_anon_rmap(struct page *page,
return;
VM_BUG_ON_PAGE(!PageLocked(page), page);
+
/* address might be in next vma when migration races vma_adjust */
if (first)
__page_set_anon_rmap(page, vma, address,
@@ -1199,10 +1219,16 @@ void page_add_new_anon_rmap(struct page *page,
VM_BUG_ON_VMA(address < vma->vm_start || address >= vma->vm_end, vma);
SetPageSwapBacked(page);
- atomic_set(&page->_mapcount, 0); /* increment count (starts at -1) */
if (compound) {
VM_BUG_ON_PAGE(!PageTransHuge(page), page);
+ /* increment count (starts at -1) */
+ atomic_set(compound_mapcount_ptr(page), 0);
__inc_zone_page_state(page, NR_ANON_TRANSPARENT_HUGEPAGES);
+ } else {
+ /* Anon THP always mapped first with PMD */
+ VM_BUG_ON_PAGE(PageTransCompound(page), page);
+ /* increment count (starts at -1) */
+ atomic_set(&page->_mapcount, 0);
}
__mod_zone_page_state(page_zone(page), NR_ANON_PAGES, nr);
__page_set_anon_rmap(page, vma, address, 1);
@@ -1232,12 +1258,15 @@ static void page_remove_file_rmap(struct page *page)
memcg = mem_cgroup_begin_page_stat(page);
- /* page still mapped by someone else? */
- if (!atomic_add_negative(-1, &page->_mapcount))
+ /* Hugepages are not counted in NR_FILE_MAPPED for now. */
+ if (unlikely(PageHuge(page))) {
+ /* hugetlb pages are always mapped with pmds */
+ atomic_dec(compound_mapcount_ptr(page));
goto out;
+ }
- /* Hugepages are not counted in NR_FILE_MAPPED for now. */
- if (unlikely(PageHuge(page)))
+ /* page still mapped by someone else? */
+ if (!atomic_add_negative(-1, &page->_mapcount))
goto out;
/*
@@ -1254,6 +1283,39 @@ out:
mem_cgroup_end_page_stat(memcg);
}
+static void page_remove_anon_compound_rmap(struct page *page)
+{
+ int i, nr;
+
+ if (!atomic_add_negative(-1, compound_mapcount_ptr(page)))
+ return;
+
+ /* Hugepages are not counted in NR_ANON_PAGES for now. */
+ if (unlikely(PageHuge(page)))
+ return;
+
+ if (!IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE))
+ return;
+
+ __dec_zone_page_state(page, NR_ANON_TRANSPARENT_HUGEPAGES);
+
+ if (TestClearPageDoubleMap(page)) {
+ /*
+ * Subpages can be mapped with PTEs too. Check how many of
+ * themi are still mapped.
+ */
+ for (i = 0, nr = 0; i < HPAGE_PMD_NR; i++) {
+ if (atomic_add_negative(-1, &page[i]._mapcount))
+ nr++;
+ }
+ } else {
+ nr = HPAGE_PMD_NR;
+ }
+
+ if (nr)
+ __mod_zone_page_state(page_zone(page), NR_ANON_PAGES, -nr);
+}
+
/**
* page_remove_rmap - take down pte mapping from a page
* @page: page to remove mapping from
@@ -1263,33 +1325,25 @@ out:
*/
void page_remove_rmap(struct page *page, bool compound)
{
- int nr = compound ? hpage_nr_pages(page) : 1;
-
if (!PageAnon(page)) {
VM_BUG_ON_PAGE(compound && !PageHuge(page), page);
page_remove_file_rmap(page);
return;
}
+ if (compound)
+ return page_remove_anon_compound_rmap(page);
+
/* page still mapped by someone else? */
if (!atomic_add_negative(-1, &page->_mapcount))
return;
- /* Hugepages are not counted in NR_ANON_PAGES for now. */
- if (unlikely(PageHuge(page)))
- return;
-
/*
* We use the irq-unsafe __{inc|mod}_zone_page_stat because
* these counters are not modified in interrupt context, and
* pte lock(a spinlock) is held, which implies preemption disabled.
*/
- if (compound) {
- VM_BUG_ON_PAGE(!PageTransHuge(page), page);
- __dec_zone_page_state(page, NR_ANON_TRANSPARENT_HUGEPAGES);
- }
-
- __mod_zone_page_state(page_zone(page), NR_ANON_PAGES, -nr);
+ __dec_zone_page_state(page, NR_ANON_PAGES);
if (unlikely(PageMlocked(page)))
clear_page_mlock(page);
@@ -1710,7 +1764,7 @@ void hugepage_add_anon_rmap(struct page *page,
BUG_ON(!PageLocked(page));
BUG_ON(!anon_vma);
/* address might be in next vma when migration races vma_adjust */
- first = atomic_inc_and_test(&page->_mapcount);
+ first = atomic_inc_and_test(compound_mapcount_ptr(page));
if (first)
__hugepage_set_anon_rmap(page, vma, address, 0);
}
@@ -1719,7 +1773,7 @@ void hugepage_add_new_anon_rmap(struct page *page,
struct vm_area_struct *vma, unsigned long address)
{
BUG_ON(address < vma->vm_start || address >= vma->vm_end);
- atomic_set(&page->_mapcount, 0);
+ atomic_set(compound_mapcount_ptr(page), 0);
__hugepage_set_anon_rmap(page, vma, address, 1);
}
#endif /* CONFIG_HUGETLB_PAGE */