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thp: file pages support for split_huge_page()

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Basic scheme is the same as for anon THP.

Main differences:

  - File pages are on radix-tree, so we have head->_count offset by
    HPAGE_PMD_NR. The count got distributed to small pages during split.

  - mapping->tree_lock prevents non-lockless access to pages under split
    over radix-tree;

  - Lockless access is prevented by setting the head->_count to 0 during
    split;

  - After split, some pages can be beyond i_size. We drop them from
    radix-tree.

  - We don't setup migration entries. Just unmap pages. It helps
    handling cases when i_size is in the middle of the page: no need
    handle unmap pages beyond i_size manually.

Link: http://lkml.kernel.org/r/1466021202-61880-20-git-send-email-kirill.shutemov@linux.intel.com
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Kirill A. Shutemov 2016-07-26 15:25:51 -07:00 committed by Linus Torvalds
parent 37f9f5595c
commit baa355fd33
2 changed files with 117 additions and 45 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
mm/gup.c
View File

@ -288,6 +288,8 @@ struct page *follow_page_mask(struct vm_area_struct *vma,
ret = split_huge_page(page);
unlock_page(page);
put_page(page);
if (pmd_none(*pmd))
return no_page_table(vma, flags);
}
return ret ? ERR_PTR(ret) :

130
mm/huge_memory.c
View File

@ -30,6 +30,7 @@
#include <linux/hashtable.h>
#include <linux/userfaultfd_k.h>
#include <linux/page_idle.h>
#include <linux/shmem_fs.h>
#include <asm/tlb.h>
#include <asm/pgalloc.h>
@ -3187,12 +3188,15 @@ void vma_adjust_trans_huge(struct vm_area_struct *vma,
static void freeze_page(struct page *page)
{
enum ttu_flags ttu_flags = TTU_MIGRATION | TTU_IGNORE_MLOCK |
TTU_IGNORE_ACCESS | TTU_RMAP_LOCKED;
enum ttu_flags ttu_flags = TTU_IGNORE_MLOCK | TTU_IGNORE_ACCESS |
TTU_RMAP_LOCKED;
int i, ret;
VM_BUG_ON_PAGE(!PageHead(page), page);
if (PageAnon(page))
ttu_flags |= TTU_MIGRATION;
/* We only need TTU_SPLIT_HUGE_PMD once */
ret = try_to_unmap(page, ttu_flags | TTU_SPLIT_HUGE_PMD);
for (i = 1; !ret && i < HPAGE_PMD_NR; i++) {
@ -3202,7 +3206,7 @@ static void freeze_page(struct page *page)
ret = try_to_unmap(page + i, ttu_flags);
}
VM_BUG_ON(ret);
VM_BUG_ON_PAGE(ret, page + i - 1);
}
static void unfreeze_page(struct page *page)
@ -3224,15 +3228,20 @@ static void __split_huge_page_tail(struct page *head, int tail,
/*
* tail_page->_refcount is zero and not changing from under us. But
* get_page_unless_zero() may be running from under us on the
* tail_page. If we used atomic_set() below instead of atomic_inc(), we
* would then run atomic_set() concurrently with
* tail_page. If we used atomic_set() below instead of atomic_inc() or
* atomic_add(), we would then run atomic_set() concurrently with
* get_page_unless_zero(), and atomic_set() is implemented in C not
* using locked ops. spin_unlock on x86 sometime uses locked ops
* because of PPro errata 66, 92, so unless somebody can guarantee
* atomic_set() here would be safe on all archs (and not only on x86),
* it's safer to use atomic_inc().
* it's safer to use atomic_inc()/atomic_add().
*/
if (PageAnon(head)) {
page_ref_inc(page_tail);
} else {
/* Additional pin to radix tree */
page_ref_add(page_tail, 2);
}
page_tail->flags &= ~PAGE_FLAGS_CHECK_AT_PREP;
page_tail->flags |= (head->flags &
@ -3268,25 +3277,44 @@ static void __split_huge_page_tail(struct page *head, int tail,
lru_add_page_tail(head, page_tail, lruvec, list);
}
static void __split_huge_page(struct page *page, struct list_head *list)
static void __split_huge_page(struct page *page, struct list_head *list,
unsigned long flags)
{
struct page *head = compound_head(page);
struct zone *zone = page_zone(head);
struct lruvec *lruvec;
pgoff_t end = -1;
int i;
/* prevent PageLRU to go away from under us, and freeze lru stats */
spin_lock_irq(&zone->lru_lock);
lruvec = mem_cgroup_page_lruvec(head, zone);
/* complete memcg works before add pages to LRU */
mem_cgroup_split_huge_fixup(head);
for (i = HPAGE_PMD_NR - 1; i >= 1; i--)
if (!PageAnon(page))
end = DIV_ROUND_UP(i_size_read(head->mapping->host), PAGE_SIZE);
for (i = HPAGE_PMD_NR - 1; i >= 1; i--) {
__split_huge_page_tail(head, i, lruvec, list);
/* Some pages can be beyond i_size: drop them from page cache */
if (head[i].index >= end) {
__ClearPageDirty(head + i);
__delete_from_page_cache(head + i, NULL);
put_page(head + i);
}
}
ClearPageCompound(head);
spin_unlock_irq(&zone->lru_lock);
/* See comment in __split_huge_page_tail() */
if (PageAnon(head)) {
page_ref_inc(head);
} else {
/* Additional pin to radix tree */
page_ref_add(head, 2);
spin_unlock(&head->mapping->tree_lock);
}
spin_unlock_irqrestore(&page_zone(head)->lru_lock, flags);
unfreeze_page(head);
@ -3411,36 +3439,54 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
{
struct page *head = compound_head(page);
struct pglist_data *pgdata = NODE_DATA(page_to_nid(head));
struct anon_vma *anon_vma;
int count, mapcount, ret;
struct anon_vma *anon_vma = NULL;
struct address_space *mapping = NULL;
int count, mapcount, extra_pins, ret;
bool mlocked;
unsigned long flags;
VM_BUG_ON_PAGE(is_huge_zero_page(page), page);
VM_BUG_ON_PAGE(!PageAnon(page), page);
VM_BUG_ON_PAGE(!PageLocked(page), page);
VM_BUG_ON_PAGE(!PageSwapBacked(page), page);
VM_BUG_ON_PAGE(!PageCompound(page), page);
if (PageAnon(head)) {
/*
* The caller does not necessarily hold an mmap_sem that would prevent
* the anon_vma disappearing so we first we take a reference to it
* and then lock the anon_vma for write. This is similar to
* page_lock_anon_vma_read except the write lock is taken to serialise
* against parallel split or collapse operations.
* The caller does not necessarily hold an mmap_sem that would
* prevent the anon_vma disappearing so we first we take a
* reference to it and then lock the anon_vma for write. This
* is similar to page_lock_anon_vma_read except the write lock
* is taken to serialise against parallel split or collapse
* operations.
*/
anon_vma = page_get_anon_vma(head);
if (!anon_vma) {
ret = -EBUSY;
goto out;
}
extra_pins = 0;
mapping = NULL;
anon_vma_lock_write(anon_vma);
} else {
mapping = head->mapping;
/* Truncated ? */
if (!mapping) {
ret = -EBUSY;
goto out;
}
/* Addidional pins from radix tree */
extra_pins = HPAGE_PMD_NR;
anon_vma = NULL;
i_mmap_lock_read(mapping);
}
/*
* Racy check if we can split the page, before freeze_page() will
* split PMDs
*/
if (total_mapcount(head) != page_count(head) - 1) {
if (total_mapcount(head) != page_count(head) - extra_pins - 1) {
ret = -EBUSY;
goto out_unlock;
}
@ -3453,35 +3499,60 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
if (mlocked)
lru_add_drain();
/* prevent PageLRU to go away from under us, and freeze lru stats */
spin_lock_irqsave(&page_zone(head)->lru_lock, flags);
if (mapping) {
void **pslot;
spin_lock(&mapping->tree_lock);
pslot = radix_tree_lookup_slot(&mapping->page_tree,
page_index(head));
/*
* Check if the head page is present in radix tree.
* We assume all tail are present too, if head is there.
*/
if (radix_tree_deref_slot_protected(pslot,
&mapping->tree_lock) != head)
goto fail;
}
/* Prevent deferred_split_scan() touching ->_refcount */
spin_lock_irqsave(&pgdata->split_queue_lock, flags);
spin_lock(&pgdata->split_queue_lock);
count = page_count(head);
mapcount = total_mapcount(head);
if (!mapcount && count == 1) {
if (!mapcount && page_ref_freeze(head, 1 + extra_pins)) {
if (!list_empty(page_deferred_list(head))) {
pgdata->split_queue_len--;
list_del(page_deferred_list(head));
}
spin_unlock_irqrestore(&pgdata->split_queue_lock, flags);
__split_huge_page(page, list);
spin_unlock(&pgdata->split_queue_lock);
__split_huge_page(page, list, flags);
ret = 0;
} else if (IS_ENABLED(CONFIG_DEBUG_VM) && mapcount) {
spin_unlock_irqrestore(&pgdata->split_queue_lock, flags);
} else {
if (IS_ENABLED(CONFIG_DEBUG_VM) && mapcount) {
pr_alert("total_mapcount: %u, page_count(): %u\n",
mapcount, count);
if (PageTail(page))
dump_page(head, NULL);
dump_page(page, "total_mapcount(head) > 0");
BUG();
} else {
spin_unlock_irqrestore(&pgdata->split_queue_lock, flags);
}
spin_unlock(&pgdata->split_queue_lock);
fail: if (mapping)
spin_unlock(&mapping->tree_lock);
spin_unlock_irqrestore(&page_zone(head)->lru_lock, flags);
unfreeze_page(head);
ret = -EBUSY;
}
out_unlock:
if (anon_vma) {
anon_vma_unlock_write(anon_vma);
put_anon_vma(anon_vma);
}
if (mapping)
i_mmap_unlock_read(mapping);
out:
count_vm_event(!ret ? THP_SPLIT_PAGE : THP_SPLIT_PAGE_FAILED);
return ret;
@ -3604,8 +3675,7 @@ static int split_huge_pages_set(void *data, u64 val)
if (zone != page_zone(page))
goto next;
if (!PageHead(page) || !PageAnon(page) ||
PageHuge(page))
if (!PageHead(page) || PageHuge(page) || !PageLRU(page))
goto next;
total++;