[PATCH] lazy freeing of memory through MADV_FREE

Rik van Riel
2007-04-17T07:15:51Z

[-- Attachment #1: Type: text/plain, Size: 1024 bytes --]

Make it possible for applications to have the kernel free memory
lazily. This reduces a repeated free/malloc cycle from freeing
pages and allocating them, to just marking them freeable. If the
application wants to reuse them before the kernel needs the memory,
not even a page fault will happen.

This patch, together with Ulrich's glibc change, increases
MySQL sysbench performance by a factor of 2 on my quad core
test system.

Signed-off-by: Rik van Riel <riel@redhat.com>

---
Ulrich Drepper has test glibc RPMS for this functionality at:

http://people.redhat.com/drepper/rpms

Andrew, I have stress tested this patch for a few days now and
have not been able to find any more bugs. I believe it is ready
to be merged in -mm, and upstream at the next merge window.

When the patch goes upstream, I will submit a small follow-up
patch to revert MADV_DONTNEED behaviour to what it did previously
and have the new behaviour trigger only on MADV_FREE: at that
point people will have to get new test RPMs of glibc.

[-- Attachment #2: linux-2.6.21-rc6-mm1-madv_free.patch --]
[-- Type: text/x-patch, Size: 11514 bytes --]

--- linux-2.6.21-rc6-mm1/include/asm-parisc/mman.h.madv_free 2007-04-17 02:17:19.000000000 -0400
+++ linux-2.6.21-rc6-mm1/include/asm-parisc/mman.h 2007-04-17 02:22:46.000000000 -0400
@@ -38,6 +38,7 @@
#define MADV_SPACEAVAIL 5 /* insure that resources are reserved */
#define MADV_VPS_PURGE 6 /* Purge pages from VM page cache */
#define MADV_VPS_INHERIT 7 /* Inherit parents page size */
+#define MADV_FREE 8 /* don't need the pages or the data */

/* common/generic parameters */
#define MADV_REMOVE 9 /* remove these pages & resources */
--- linux-2.6.21-rc6-mm1/include/asm-mips/mman.h.madv_free 2007-04-17 02:17:19.000000000 -0400
+++ linux-2.6.21-rc6-mm1/include/asm-mips/mman.h 2007-04-17 02:22:46.000000000 -0400
@@ -65,6 +65,7 @@
#define MADV_SEQUENTIAL 2 /* expect sequential page references */
#define MADV_WILLNEED 3 /* will need these pages */
#define MADV_DONTNEED 4 /* don't need these pages */
+#define MADV_FREE 5 /* don't need the pages or the data */

/* common parameters: try to keep these consistent across architectures */
#define MADV_REMOVE 9 /* remove these pages & resources */
--- linux-2.6.21-rc6-mm1/include/asm-xtensa/mman.h.madv_free 2007-04-17 02:17:19.000000000 -0400
+++ linux-2.6.21-rc6-mm1/include/asm-xtensa/mman.h 2007-04-17 02:22:46.000000000 -0400
@@ -72,6 +72,7 @@
#define MADV_SEQUENTIAL 2 /* expect sequential page references */
#define MADV_WILLNEED 3 /* will need these pages */
#define MADV_DONTNEED 4 /* don't need these pages */
+#define MADV_FREE 5 /* don't need the pages or the data */

/* common parameters: try to keep these consistent across architectures */
#define MADV_REMOVE 9 /* remove these pages & resources */
--- linux-2.6.21-rc6-mm1/include/linux/swap.h.madv_free 2007-04-17 02:17:43.000000000 -0400
+++ linux-2.6.21-rc6-mm1/include/linux/swap.h 2007-04-17 02:22:46.000000000 -0400
@@ -182,6 +182,7 @@ extern void FASTCALL(lru_cache_add(struc
extern void FASTCALL(lru_cache_add_active(struct page *));
extern void FASTCALL(lru_cache_add_tail(struct page *));
extern void FASTCALL(activate_page(struct page *));
+extern void FASTCALL(deactivate_tail_page(struct page *));
extern void FASTCALL(mark_page_accessed(struct page *));
extern void lru_add_drain(void);
extern int lru_add_drain_all(void);
--- linux-2.6.21-rc6-mm1/include/linux/mm.h.madv_free 2007-04-17 02:17:43.000000000 -0400
+++ linux-2.6.21-rc6-mm1/include/linux/mm.h 2007-04-17 02:22:46.000000000 -0400
@@ -767,6 +767,7 @@ struct zap_details {
pgoff_t last_index; /* Highest page->index to unmap */
spinlock_t *i_mmap_lock; /* For unmap_mapping_range: */
unsigned long truncate_count; /* Compare vm_truncate_count */
+ short madv_free; /* MADV_FREE anonymous memory */
};

struct page *vm_normal_page(struct vm_area_struct *, unsigned long, pte_t);
--- linux-2.6.21-rc6-mm1/include/linux/page-flags.h.madv_free 2007-04-17 02:17:43.000000000 -0400
+++ linux-2.6.21-rc6-mm1/include/linux/page-flags.h 2007-04-17 02:23:16.000000000 -0400
@@ -91,6 +91,7 @@
#define PG_booked 20 /* Has blocks reserved on-disk */

#define PG_readahead 21 /* Reminder to do read-ahead */
+#define PG_lazyfree 22 /* MADV_FREE potential throwaway */

/* PG_owner_priv_1 users should have descriptive aliases */
#define PG_checked PG_owner_priv_1 /* Used by some filesystems */
@@ -216,6 +217,11 @@ static inline void SetPageUptodate(struc
#define ClearPageReclaim(page) clear_bit(PG_reclaim, &(page)->flags)
#define TestClearPageReclaim(page) test_and_clear_bit(PG_reclaim, &(page)->flags)

+#define PageLazyFree(page) test_bit(PG_lazyfree, &(page)->flags)
+#define SetPageLazyFree(page) set_bit(PG_lazyfree, &(page)->flags)
+#define ClearPageLazyFree(page) clear_bit(PG_lazyfree, &(page)->flags)
+#define __ClearPageLazyFree(page) __clear_bit(PG_lazyfree, &(page)->flags)
+
#define PageCompound(page) test_bit(PG_compound, &(page)->flags)
#define __SetPageCompound(page) __set_bit(PG_compound, &(page)->flags)
#define __ClearPageCompound(page) __clear_bit(PG_compound, &(page)->flags)
--- linux-2.6.21-rc6-mm1/include/asm-alpha/mman.h.madv_free 2007-04-17 02:17:19.000000000 -0400
+++ linux-2.6.21-rc6-mm1/include/asm-alpha/mman.h 2007-04-17 02:22:46.000000000 -0400
@@ -42,6 +42,7 @@
#define MADV_WILLNEED 3 /* will need these pages */
#define MADV_SPACEAVAIL 5 /* ensure resources are available */
#define MADV_DONTNEED 6 /* don't need these pages */
+#define MADV_FREE 7 /* don't need the pages or the data */

/* common/generic parameters */
#define MADV_REMOVE 9 /* remove these pages & resources */
--- linux-2.6.21-rc6-mm1/include/asm-generic/mman.h.madv_free 2007-04-17 02:17:19.000000000 -0400
+++ linux-2.6.21-rc6-mm1/include/asm-generic/mman.h 2007-04-17 02:22:46.000000000 -0400
@@ -29,6 +29,7 @@
#define MADV_SEQUENTIAL 2 /* expect sequential page references */
#define MADV_WILLNEED 3 /* will need these pages */
#define MADV_DONTNEED 4 /* don't need these pages */
+#define MADV_FREE 5 /* don't need the pages or the data */

/* common parameters: try to keep these consistent across architectures */
#define MADV_REMOVE 9 /* remove these pages & resources */
--- linux-2.6.21-rc6-mm1/mm/memory.c.madv_free 2007-04-17 02:17:43.000000000 -0400
+++ linux-2.6.21-rc6-mm1/mm/memory.c 2007-04-17 02:22:46.000000000 -0400
@@ -432,6 +432,7 @@ copy_one_pte(struct mm_struct *dst_mm, s
unsigned long vm_flags = vma->vm_flags;
pte_t pte = *src_pte;
struct page *page;
+ int dirty = 0;

/* pte contains position in swap or file, so copy. */
if (unlikely(!pte_present(pte))) {
@@ -466,6 +467,7 @@ copy_one_pte(struct mm_struct *dst_mm, s
* in the parent and the child
*/
if (is_cow_mapping(vm_flags)) {
+ dirty = pte_dirty(pte);
ptep_set_wrprotect(src_mm, addr, src_pte);
pte = pte_wrprotect(pte);
}
@@ -483,6 +485,8 @@ copy_one_pte(struct mm_struct *dst_mm, s
get_page(page);
page_dup_rmap(page, vma, addr);
rss[!!PageAnon(page)]++;
+ if (dirty && PageLazyFree(page))
+ ClearPageLazyFree(page);
}

out_set_pte:
@@ -661,6 +665,25 @@ static unsigned long zap_pte_range(struc
(page->index < details->first_index ||
page->index > details->last_index))
continue;
+
+ /*
+ * MADV_FREE is used to lazily recycle
+ * anon memory. The process no longer
+ * needs the data and wants to avoid IO.
+ */
+ if (details->madv_free && PageAnon(page)) {
+ if (unlikely(PageSwapCache(page)) &&
+ !TestSetPageLocked(page)) {
+ remove_exclusive_swap_page(page);
+ unlock_page(page);
+ }
+ ptep_clear_flush_dirty(vma, addr, pte);
+ ptep_clear_flush_young(vma, addr, pte);
+ SetPageLazyFree(page);
+ if (PageActive(page))
+ deactivate_tail_page(page);
+ continue;
+ }
}
ptent = ptep_get_and_clear_full(mm, addr, pte,
tlb->fullmm);
@@ -689,7 +713,8 @@ static unsigned long zap_pte_range(struc
* If details->check_mapping, we leave swap entries;
* if details->nonlinear_vma, we leave file entries.
*/
- if (unlikely(details))
+ if (unlikely(details && (details->check_mapping ||
+ details->nonlinear_vma)))
continue;
if (!pte_file(ptent))
free_swap_and_cache(pte_to_swp_entry(ptent));
@@ -755,7 +780,8 @@ static unsigned long unmap_page_range(st
pgd_t *pgd;
unsigned long next;

- if (details && !details->check_mapping && !details->nonlinear_vma)
+ if (details && !details->check_mapping && !details->nonlinear_vma
+ && !details->madv_free)
details = NULL;

BUG_ON(addr >= end);
--- linux-2.6.21-rc6-mm1/mm/page_alloc.c.madv_free 2007-04-17 02:17:43.000000000 -0400
+++ linux-2.6.21-rc6-mm1/mm/page_alloc.c 2007-04-17 02:22:46.000000000 -0400
@@ -266,6 +266,7 @@ static void bad_page(struct page *page)
1 << PG_slab |
1 << PG_swapcache |
1 << PG_writeback |
+ 1 << PG_lazyfree |
1 << PG_buddy );
set_page_count(page, 0);
reset_page_mapcount(page);
@@ -514,6 +515,8 @@ static inline int free_pages_check(struc
bad_page(page);
if (PageDirty(page))
__ClearPageDirty(page);
+ if (PageLazyFree(page))
+ __ClearPageLazyFree(page);
/*
* For now, we report if PG_reserved was found set, but do not
* clear it, and do not free the page. But we shall soon need
@@ -661,6 +664,7 @@ static int prep_new_page(struct page *pa
1 << PG_swapcache |
1 << PG_writeback |
1 << PG_reserved |
+ 1 << PG_lazyfree |
1 << PG_buddy ))))
bad_page(page);

--- linux-2.6.21-rc6-mm1/mm/swap.c.madv_free 2007-04-17 02:17:43.000000000 -0400
+++ linux-2.6.21-rc6-mm1/mm/swap.c 2007-04-17 02:22:46.000000000 -0400
@@ -152,6 +152,20 @@ void fastcall activate_page(struct page
spin_unlock_irq(&zone->lru_lock);
}

+void fastcall deactivate_tail_page(struct page *page)
+{
+ struct zone *zone = page_zone(page);
+
+ spin_lock_irq(&zone->lru_lock);
+ if (PageLRU(page) && PageActive(page)) {
+ del_page_from_active_list(zone, page);
+ ClearPageActive(page);
+ add_page_to_inactive_list_tail(zone, page);
+ __count_vm_event(PGDEACTIVATE);
+ }
+ spin_unlock_irq(&zone->lru_lock);
+}
+
/*
* Mark a page as having seen activity.
*
--- linux-2.6.21-rc6-mm1/mm/vmscan.c.madv_free 2007-04-17 02:17:43.000000000 -0400
+++ linux-2.6.21-rc6-mm1/mm/vmscan.c 2007-04-17 02:22:46.000000000 -0400
@@ -460,6 +460,24 @@ static unsigned long shrink_page_list(st

sc->nr_scanned++;

+ /*
+ * MADV_DONTNEED pages get reclaimed lazily, unless the
+ * process reuses it before we get to it.
+ */
+ if (PageLazyFree(page)) {
+ switch (try_to_unmap(page, 0)) {
+ case SWAP_FAIL:
+ ClearPageLazyFree(page);
+ goto activate_locked;
+ case SWAP_AGAIN:
+ ClearPageLazyFree(page);
+ goto keep_locked;
+ case SWAP_SUCCESS:
+ ClearPageLazyFree(page);
+ goto free_it;
+ }
+ }
+
if (!sc->may_swap && page_mapped(page))
goto keep_locked;

--- linux-2.6.21-rc6-mm1/mm/madvise.c.madv_free 2007-04-17 02:17:20.000000000 -0400
+++ linux-2.6.21-rc6-mm1/mm/madvise.c 2007-04-17 02:22:46.000000000 -0400
@@ -142,8 +142,12 @@ static long madvise_dontneed(struct vm_a
.last_index = ULONG_MAX,
};
zap_page_range(vma, start, end - start, &details);
- } else
- zap_page_range(vma, start, end - start, NULL);
+ } else {
+ struct zap_details details = {
+ .madv_free = 1,
+ };
+ zap_page_range(vma, start, end - start, &details);
+ }
return 0;
}

@@ -215,7 +219,9 @@ madvise_vma(struct vm_area_struct *vma,
error = madvise_willneed(vma, prev, start, end);
break;

+ /* FIXME: POSIX says that MADV_DONTNEED cannot throw away data. */
case MADV_DONTNEED:
+ case MADV_FREE:
error = madvise_dontneed(vma, prev, start, end);
break;

--- linux-2.6.21-rc6-mm1/mm/rmap.c.madv_free 2007-04-17 02:17:43.000000000 -0400
+++ linux-2.6.21-rc6-mm1/mm/rmap.c 2007-04-17 02:22:46.000000000 -0400
@@ -707,7 +707,17 @@ static int try_to_unmap_one(struct page
/* Update high watermark before we lower rss */
update_hiwater_rss(mm);

- if (PageAnon(page)) {
+ /* MADV_FREE is used to lazily free memory from userspace. */
+ if (PageLazyFree(page) && !migration) {
+ /* There is new data in the page. Reinstate it. */
+ if (unlikely(pte_dirty(pteval))) {
+ set_pte_at(mm, address, pte, pteval);
+ ret = SWAP_FAIL;
+ goto out_unmap;
+ }
+ /* Throw the page away. */
+ dec_mm_counter(mm, anon_rss);
+ } else if (PageAnon(page)) {
swp_entry_t entry = { .val = page_private(page) };

if (PageSwapCache(page)) {