On Mon, Aug 20, 2012 at 09:43:02AM -0700, Tim Chen wrote:
> > In shrink_page_list, call to page_referenced_file will causes the
> > acquisition/release of mapping->i_mmap_mutex for each page in the page
> > list. However, it is very likely that successive pages in the list
> > share the same mapping and we can reduce the frequency of i_mmap_mutex
> > acquisition by holding the mutex in shrink_page_list. This improves the
> > performance when the system has a lot page reclamations for file mapped
> > pages if workloads are using a lot of memory for page cache.
Is there a (performant) way to avoid passing around the
'mmap_mutex_locked' state?
For example, does it hurt to have all the callers hold the i_mmap_mutex()
over the entire call, or do we rely on being able to execute large chunks
of this in parallel?
Here's what I'm thinking:
1. Rename the existing page_referenced implementation to __page_referenced().
2. Add:
int needs_page_mmap_mutex(struct page *page)
{
return page->mapping && page_mapped(page) && page_rmapping(page) &&
!PageKsm(page) && !PageAnon(page);
}
int page_referenced(struct page *page, int is_locked, struct mem_cgroup *memcg,
unsigned long *vm_flags)
{
int result, needs_lock;
needs_lock = needs_page_mmap_mutex(page);
if (needs_lock)
mutex_lock(&page->mapping->i_mmap_mutex);
result = __page_referenced(page, is_locked, memcg, vm_flags);
if (needs_lock)
mutex_unlock(&page->mapping->i_mmap_mutex);
return result;
}
3. Rename the existing try_to_unmap() to __try_to_unmap()
4. Add:
int try_to_unmap(struct page *page, enum ttu_flags flags)
{
int result, needs_lock;
needs_lock = needs_page_mmap_mutex(page);
if (needs_lock)
mutex_lock(&page->mapping->i_mmap_mutex);
result = __try_to_unmap(page, is_locked, memcg, vm_flags);
if (needs_lock)
mutex_unlock(&page->mapping->i_mmap_mutex);
return result;
}
5. Change page_check_references to always call __page_referenced (since it
now always holds the mutex)
6. Replace the mutex_lock() calls in page_referenced_file() and
try_to_unmap_file() with
BUG_ON(!mutex_is_locked(&mapping->i_mmap_mutex));
7. I think you can simplify this:
> - references = page_check_references(page, mz, sc);
> + if (page->mapping) {
> + if (i_mmap_mutex == &page->mapping->i_mmap_mutex) {
> + mmap_mutex_locked = 1;
> + } else {
> + if (page_mapped(page) && page_rmapping(page)
> + && !PageKsm(page) && !PageAnon(page)) {
> + if (i_mmap_mutex)
> + mutex_unlock(i_mmap_mutex);
> + i_mmap_mutex =
> &page->mapping->i_mmap_mutex;
> + mutex_lock(i_mmap_mutex);
> + mmap_mutex_locked = 1;
> + }
> + }
> + }
> +
> + references = page_check_references(page, mz, sc,
> + mmap_mutex_locked);
to just:
+ if (needs_page_mmap_mutex(page) &&
+ i_mmap_mutex != &page->mapping->i_mmap_mutex) {
+ if (i_mmap_mutex)
+ mutex_unlock(i_mmap_mutex);
+ i_mmap_mutex = &page->mapping->i_mmap_mutex;
+ mutex_lock(i_mmap_mutex);
+ }
references = page_check_references(page, mz, sc);
The only clunky bit would seem to be this bit:
> if (page_mapped(page) && mapping) {
> - switch (try_to_unmap(page, TTU_UNMAP)) {
> + switch (try_to_unmap(page, TTU_UNMAP,
> + mmap_mutex_locked)) {
Which I think has to look like this:
if (page_mapped(page) && mapping) {
- switch (try_to_unmap(page, TTU_UNMAP)) {
+ int result;
+ if (i_mmap_mutex)
+ result = __try_to_unmap(page, TTU_UNMAP);
+ else
+ result = try_to_unmap(page, TTU_UNMAP);
+ switch (result) {
Either that, or use a function pointer. But ... bleugh.
> diff --git a/include/linux/rmap.h b/include/linux/rmap.h
> index fd07c45..f0174ae 100644
> --- a/include/linux/rmap.h
> +++ b/include/linux/rmap.h
> @@ -156,8 +156,8 @@ 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 *memcg, unsigned long *vm_flags);
> +int page_referenced(struct page *, int is_locked, struct mem_cgroup *memcg,
> + unsigned long *vm_flags, int mmap_mutex_locked);
> int page_referenced_one(struct page *, struct vm_area_struct *,
> unsigned long address, unsigned int *mapcount, unsigned long *vm_flags);
>
> @@ -175,7 +175,7 @@ enum ttu_flags {
>
> bool is_vma_temporary_stack(struct vm_area_struct *vma);
>
> -int try_to_unmap(struct page *, enum ttu_flags flags);
> +int try_to_unmap(struct page *, enum ttu_flags flags, int mmap_mutex_locked);
> int try_to_unmap_one(struct page *, struct vm_area_struct *,
> unsigned long address, enum ttu_flags flags);
>
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 97cc273..5f162c7 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -953,7 +953,7 @@ static int hwpoison_user_mappings(struct page *p,
> unsigned long pfn,
> if (hpage != ppage)
> lock_page(ppage);
>
> - ret = try_to_unmap(ppage, ttu);
> + ret = try_to_unmap(ppage, ttu, 0);
> if (ret != SWAP_SUCCESS)
> printk(KERN_ERR "MCE %#lx: failed to unmap page
> (mapcount=%d)\n",
> pfn, page_mapcount(ppage));
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 1107238..1aa37b1 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -802,7 +802,7 @@ static int __unmap_and_move(struct page *page, struct
> page *newpage,
> }
>
> /* Establish migration ptes or remove ptes */
> - try_to_unmap(page, TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS);
> + try_to_unmap(page, TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS, 0);
>
> skip_unmap:
> if (!page_mapped(page))
> @@ -918,7 +918,8 @@ static int unmap_and_move_huge_page(new_page_t
> get_new_page,
> if (PageAnon(hpage))
> anon_vma = page_get_anon_vma(hpage);
>
> - try_to_unmap(hpage, TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS);
> + try_to_unmap(hpage,
> + TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS, 0);
>
> if (!page_mapped(hpage))
> rc = move_to_new_page(new_hpage, hpage, 1, mode);
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 5b5ad58..63fc84b 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -820,7 +820,7 @@ static int page_referenced_anon(struct page *page,
> */
> static int page_referenced_file(struct page *page,
> struct mem_cgroup *memcg,
> - unsigned long *vm_flags)
> + unsigned long *vm_flags, int mmap_mutex_locked)
> {
> unsigned int mapcount;
> struct address_space *mapping = page->mapping;
> @@ -844,7 +844,8 @@ static int page_referenced_file(struct page *page,
> */
> BUG_ON(!PageLocked(page));
>
> - mutex_lock(&mapping->i_mmap_mutex);
> + if (!mmap_mutex_locked)
> + mutex_lock(&mapping->i_mmap_mutex);
>
> /*
> * i_mmap_mutex does not stabilize mapcount at all, but mapcount
> @@ -869,7 +870,8 @@ static int page_referenced_file(struct page *page,
> break;
> }
>
> - mutex_unlock(&mapping->i_mmap_mutex);
> + if (!mmap_mutex_locked)
> + mutex_unlock(&mapping->i_mmap_mutex);
> return referenced;
> }
>
> @@ -886,7 +888,7 @@ static int page_referenced_file(struct page *page,
> int page_referenced(struct page *page,
> int is_locked,
> struct mem_cgroup *memcg,
> - unsigned long *vm_flags)
> + unsigned long *vm_flags, int mmap_mutex_locked)
> {
> int referenced = 0;
> int we_locked = 0;
> @@ -908,7 +910,7 @@ int page_referenced(struct page *page,
> vm_flags);
> else if (page->mapping)
> referenced += page_referenced_file(page, memcg,
> - vm_flags);
> + vm_flags, mmap_mutex_locked);
> if (we_locked)
> unlock_page(page);
>
> @@ -1548,7 +1550,8 @@ static int try_to_unmap_anon(struct page *page, enum
> ttu_flags flags)
> * vm_flags for that VMA. That should be OK, because that vma shouldn't be
> * 'LOCKED.
> */
> -static int try_to_unmap_file(struct page *page, enum ttu_flags flags)
> +static int try_to_unmap_file(struct page *page, enum ttu_flags flags,
> + int mmap_mutex_locked)
> {
> struct address_space *mapping = page->mapping;
> pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
> @@ -1560,7 +1563,8 @@ static int try_to_unmap_file(struct page *page, enum
> ttu_flags flags)
> unsigned long max_nl_size = 0;
> unsigned int mapcount;
>
> - mutex_lock(&mapping->i_mmap_mutex);
> + if (!mmap_mutex_locked)
> + mutex_lock(&mapping->i_mmap_mutex);
> vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) {
> unsigned long address = vma_address(page, vma);
> if (address == -EFAULT)
> @@ -1640,7 +1644,8 @@ static int try_to_unmap_file(struct page *page, enum
> ttu_flags flags)
> list_for_each_entry(vma, &mapping->i_mmap_nonlinear, shared.vm_set.list)
> vma->vm_private_data = NULL;
> out:
> - mutex_unlock(&mapping->i_mmap_mutex);
> + if (!mmap_mutex_locked)
> + mutex_unlock(&mapping->i_mmap_mutex);
> return ret;
> }
>
> @@ -1658,7 +1663,7 @@ out:
> * SWAP_FAIL - the page is unswappable
> * SWAP_MLOCK - page is mlocked.
> */
> -int try_to_unmap(struct page *page, enum ttu_flags flags)
> +int try_to_unmap(struct page *page, enum ttu_flags flags, int
> mmap_mutex_locked)
> {
> int ret;
>
> @@ -1670,7 +1675,7 @@ int try_to_unmap(struct page *page, enum ttu_flags
> flags)
> else if (PageAnon(page))
> ret = try_to_unmap_anon(page, flags);
> else
> - ret = try_to_unmap_file(page, flags);
> + ret = try_to_unmap_file(page, flags, mmap_mutex_locked);
> if (ret != SWAP_MLOCK && !page_mapped(page))
> ret = SWAP_SUCCESS;
> return ret;
> @@ -1700,7 +1705,7 @@ int try_to_munlock(struct page *page)
> else if (PageAnon(page))
> return try_to_unmap_anon(page, TTU_MUNLOCK);
> else
> - return try_to_unmap_file(page, TTU_MUNLOCK);
> + return try_to_unmap_file(page, TTU_MUNLOCK, 0);
> }
>
> void __put_anon_vma(struct anon_vma *anon_vma)
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index a538565..1af1f1c 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -27,6 +27,7 @@
> buffer_heads_over_limit */
> #include <linux/mm_inline.h>
> #include <linux/backing-dev.h>
> +#include <linux/ksm.h>
> #include <linux/rmap.h>
> #include <linux/topology.h>
> #include <linux/cpu.h>
> @@ -781,12 +782,14 @@ enum page_references {
>
> static enum page_references page_check_references(struct page *page,
> struct mem_cgroup_zone *mz,
> - struct scan_control *sc)
> + struct scan_control *sc,
> + int mmap_mutex_locked)
> {
> int referenced_ptes, referenced_page;
> unsigned long vm_flags;
>
> - referenced_ptes = page_referenced(page, 1, mz->mem_cgroup, &vm_flags);
> + referenced_ptes = page_referenced(page, 1, mz->mem_cgroup, &vm_flags,
> + mmap_mutex_locked);
> referenced_page = TestClearPageReferenced(page);
>
> /* Lumpy reclaim - ignore references */
> @@ -856,6 +859,7 @@ static unsigned long shrink_page_list(struct list_head
> *page_list,
> unsigned long nr_congested = 0;
> unsigned long nr_reclaimed = 0;
> unsigned long nr_writeback = 0;
> + struct mutex *i_mmap_mutex = NULL;
>
> cond_resched();
>
> @@ -865,12 +869,14 @@ static unsigned long shrink_page_list(struct list_head
> *page_list,
> struct address_space *mapping;
> struct page *page;
> int may_enter_fs;
> + int mmap_mutex_locked;
>
> cond_resched();
>
> page = lru_to_page(page_list);
> list_del(&page->lru);
>
> + mmap_mutex_locked = 0;
> if (!trylock_page(page))
> goto keep;
>
> @@ -909,7 +915,23 @@ static unsigned long shrink_page_list(struct list_head
> *page_list,
> }
> }
>
> - references = page_check_references(page, mz, sc);
> + if (page->mapping) {
> + if (i_mmap_mutex == &page->mapping->i_mmap_mutex) {
> + mmap_mutex_locked = 1;
> + } else {
> + if (page_mapped(page) && page_rmapping(page)
> + && !PageKsm(page) && !PageAnon(page)) {
> + if (i_mmap_mutex)
> + mutex_unlock(i_mmap_mutex);
> + i_mmap_mutex =
> &page->mapping->i_mmap_mutex;
> + mutex_lock(i_mmap_mutex);
> + mmap_mutex_locked = 1;
> + }
> + }
> + }
> +
> + references = page_check_references(page, mz, sc,
> + mmap_mutex_locked);
> switch (references) {
> case PAGEREF_ACTIVATE:
> goto activate_locked;
> @@ -939,7 +961,8 @@ static unsigned long shrink_page_list(struct list_head
> *page_list,
> * processes. Try to unmap it here.
> */
> if (page_mapped(page) && mapping) {
> - switch (try_to_unmap(page, TTU_UNMAP)) {
> + switch (try_to_unmap(page, TTU_UNMAP,
> + mmap_mutex_locked)) {
> case SWAP_FAIL:
> goto activate_locked;
> case SWAP_AGAIN:
> @@ -1090,6 +1113,8 @@ keep_lumpy:
> VM_BUG_ON(PageLRU(page) || PageUnevictable(page));
> }
>
> + if (i_mmap_mutex)
> + mutex_unlock(i_mmap_mutex);
> nr_reclaimed += __remove_mapping_batch(&unmap_pages, &ret_pages,
> &free_pages);
>
> @@ -1818,7 +1843,7 @@ static void shrink_active_list(unsigned long nr_to_scan,
> }
> }
>
> - if (page_referenced(page, 0, mz->mem_cgroup, &vm_flags)) {
> + if (page_referenced(page, 0, mz->mem_cgroup, &vm_flags, 0)) {
> nr_rotated += hpage_nr_pages(page);
> /*
> * Identify referenced, file-backed active pages and
>
--
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