Nick Piggin wrote:
The lazy freeing is aimed at avoiding page faults on memory
that is freed and later realloced, which is quite a common
thing in many workloads.
I would be interested to see how it performs and what these
workloads look like, although we do need to fix the basic glibc and
madvise locking problems first.
The attached graph are results of running the MySQL sysbench
workload on my quad core system. As you can see, performance
with #threads == #cpus (4) almost doubles from 1070 transactions
per second to 2014 transactions/second.
On the high end (16 threads on 4 cpus), performance increases
from 778 transactions/second on vanilla to 1310 transactions/second.
I have also benchmarked running Ulrich's changed glibc on a vanilla
kernel, which gives results somewhere in-between, but much closer to
just the vanilla kernel.
--
Politics is the struggle between those who want to make their country
the best in the world, and those who believe it already is. Each group
calls the other unpatriotic.
--- linux-2.6.20.noarch/include/asm-alpha/mman.h.madvise 2007-04-04 16:44:50.000000000 -0400
+++ linux-2.6.20.noarch/include/asm-alpha/mman.h 2007-04-04 16:56:24.000000000 -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-2.6.20.noarch/include/asm-generic/mman.h.madvise 2007-04-04 16:44:50.000000000 -0400
+++ linux-2.6.20.noarch/include/asm-generic/mman.h 2007-04-04 16:56:53.000000000 -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-2.6.20.noarch/include/asm-mips/mman.h.madvise 2007-04-04 16:44:50.000000000 -0400
+++ linux-2.6.20.noarch/include/asm-mips/mman.h 2007-04-04 16:58:02.000000000 -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-2.6.20.noarch/include/asm-parisc/mman.h.madvise 2007-04-04 16:44:50.000000000 -0400
+++ linux-2.6.20.noarch/include/asm-parisc/mman.h 2007-04-04 16:58:40.000000000 -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-2.6.20.noarch/include/asm-xtensa/mman.h.madvise 2007-04-04 16:44:51.000000000 -0400
+++ linux-2.6.20.noarch/include/asm-xtensa/mman.h 2007-04-04 16:59:14.000000000 -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-2.6.20.noarch/include/linux/mm_inline.h.madvise 2007-04-03 22:53:25.000000000 -0400
+++ linux-2.6.20.noarch/include/linux/mm_inline.h 2007-04-04 22:19:24.000000000 -0400
@@ -13,6 +13,13 @@ add_page_to_inactive_list(struct zone *z
}
static inline void
+add_page_to_inactive_list_tail(struct zone *zone, struct page *page)
+{
+ list_add_tail(&page->lru, &zone->inactive_list);
+ __inc_zone_state(zone, NR_INACTIVE);
+}
+
+static inline void
del_page_from_active_list(struct zone *zone, struct page *page)
{
list_del(&page->lru);
--- linux-2.6.20.noarch/include/linux/mm.h.madvise 2007-04-03 22:53:25.000000000 -0400
+++ linux-2.6.20.noarch/include/linux/mm.h 2007-04-04 22:06:45.000000000 -0400
@@ -716,6 +716,7 @@ 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-2.6.20.noarch/include/linux/page-flags.h.madvise 2007-04-03 22:54:58.000000000 -0400
+++ linux-2.6.20.noarch/include/linux/page-flags.h 2007-04-05 01:27:38.000000000 -0400
@@ -91,6 +91,8 @@
#define PG_nosave_free 18 /* Used for system suspend/resume */
#define PG_buddy 19 /* Page is free, on buddy lists */
+#define PG_lazyfree 20 /* MADV_FREE potential throwaway */
+
/* PG_owner_priv_1 users should have descriptive aliases */
#define PG_checked PG_owner_priv_1 /* Used by some filesystems */
@@ -237,6 +239,11 @@ 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-2.6.20.noarch/include/linux/swap.h.madvise 2007-04-05 00:29:40.000000000 -0400
+++ linux-2.6.20.noarch/include/linux/swap.h 2007-04-06 17:19:20.000000000 -0400
@@ -181,6 +181,7 @@ extern unsigned int nr_free_pagecache_pa
extern void FASTCALL(lru_cache_add(struct page *));
extern void FASTCALL(lru_cache_add_active(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-2.6.20.noarch/mm/madvise.c.madvise 2007-04-03 21:53:47.000000000 -0400
+++ linux-2.6.20.noarch/mm/madvise.c 2007-04-04 23:48:34.000000000 -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;
}
@@ -209,7 +213,9 @@ 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-2.6.20.noarch/mm/memory.c.madvise 2007-04-03 21:53:47.000000000 -0400
+++ linux-2.6.20.noarch/mm/memory.c 2007-04-06 17:18:23.000000000 -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);
rss[!!PageAnon(page)]++;
+ if (dirty && PageLazyFree(page))
+ ClearPageLazyFree(page);
}
out_set_pte:
@@ -661,6 +665,26 @@ 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);
+ }
+ /* Optimize this... */
+ 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->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-2.6.20.noarch/mm/page_alloc.c.madvise 2007-04-03 21:53:47.000000000 -0400
+++ linux-2.6.20.noarch/mm/page_alloc.c 2007-04-05 01:27:55.000000000 -0400
@@ -203,6 +203,7 @@ 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);
@@ -442,6 +443,8 @@ 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
@@ -588,6 +591,7 @@ 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-2.6.20.noarch/mm/rmap.c.madvise 2007-04-03 21:53:47.000000000 -0400
+++ linux-2.6.20.noarch/mm/rmap.c 2007-04-04 23:53:29.000000000 -0400
@@ -656,7 +656,17 @@ 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)) {
--- linux-2.6.20.noarch/mm/swap.c.madvise 2007-04-03 21:53:47.000000000 -0400
+++ linux-2.6.20.noarch/mm/swap.c 2007-04-04 23:33:27.000000000 -0400
@@ -151,6 +151,20 @@ 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-2.6.20.noarch/mm/vmscan.c.madvise 2007-04-03 21:53:47.000000000 -0400
+++ linux-2.6.20.noarch/mm/vmscan.c 2007-04-04 03:34:56.000000000 -0400
@@ -473,6 +473,24 @@ 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;
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