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authorWu Fengguang <fengguang.wu@intel.com>2009-06-16 15:33:12 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2009-06-16 19:47:44 -0700
commit8cab4754d24a0f2e05920170c845bd84472814c6 (patch)
tree99b1ec52daf8b81034f634777d2f24dd20d6d7c5
parent6fe6b7e35785e3232ffe7f81d3893f1316710a02 (diff)
vmscan: make mapped executable pages the first class citizen
Protect referenced PROT_EXEC mapped pages from being deactivated. PROT_EXEC(or its internal presentation VM_EXEC) pages normally belong to some currently running executables and their linked libraries, they shall really be cached aggressively to provide good user experiences. Thanks to Johannes Weiner for the advice to reuse the VMA walk in page_referenced() to get the PROT_EXEC bit. [more details] ( The consequences of this patch will have to be discussed together with Rik van Riel's recent patch "vmscan: evict use-once pages first". ) ( Some of the good points and insights are taken into this changelog. Thanks to all the involved people for the great LKML discussions. ) the problem =========== For a typical desktop, the most precious working set is composed of *actively accessed* (1) memory mapped executables (2) and their anonymous pages (3) and other files (4) and the dcache/icache/.. slabs while the least important data are (5) infrequently used or use-once files For a typical desktop, one major problem is busty and large amount of (5) use-once files flushing out the working set. Inside the working set, (4) dcache/icache have already been too sticky ;-) So we only have to care (2) anonymous and (1)(3) file pages. anonymous pages =============== Anonymous pages are effectively immune to the streaming IO attack, because we now have separate file/anon LRU lists. When the use-once files crowd into the file LRU, the list's "quality" is significantly lowered. Therefore the scan balance policy in get_scan_ratio() will choose to scan the (low quality) file LRU much more frequently than the anon LRU. file pages ========== Rik proposed to *not* scan the active file LRU when the inactive list grows larger than active list. This guarantees that when there are use-once streaming IO, and the working set is not too large(so that active_size < inactive_size), the active file LRU will *not* be scanned at all. So the not-too-large working set can be well protected. But there are also situations where the file working set is a bit large so that (active_size >= inactive_size), or the streaming IOs are not purely use-once. In these cases, the active list will be scanned slowly. Because the current shrink_active_list() policy is to deactivate active pages regardless of their referenced bits. The deactivated pages become susceptible to the streaming IO attack: the inactive list could be scanned fast (500MB / 50MBps = 10s) so that the deactivated pages don't have enough time to get re-referenced. Because a user tend to switch between windows in intervals from seconds to minutes. This patch holds mapped executable pages in the active list as long as they are referenced during each full scan of the active list. Because the active list is normally scanned much slower, they get longer grace time (eg. 100s) for further references, which better matches the pace of user operations. Therefore this patch greatly prolongs the in-cache time of executable code, when there are moderate memory pressures. before patch: guaranteed to be cached if reference intervals < I after patch: guaranteed to be cached if reference intervals < I+A (except when randomly reclaimed by the lumpy reclaim) where A = time to fully scan the active file LRU I = time to fully scan the inactive file LRU Note that normally A >> I. side effects ============ This patch is safe in general, it restores the pre-2.6.28 mmap() behavior but in a much smaller and well targeted scope. One may worry about some one to abuse the PROT_EXEC heuristic. But as Andrew Morton stated, there are other tricks to getting that sort of boost. Another concern is the PROT_EXEC mapped pages growing large in rare cases, and therefore hurting reclaim efficiency. But a sane application targeted for large audience will never use PROT_EXEC for data mappings. If some home made application tries to abuse that bit, it shall be aware of the consequences. If it is abused to scale of 2/3 total memory, it gains nothing but overheads. benchmarks ========== 1) memory tight desktop 1.1) brief summary - clock time and major faults are reduced by 50%; - pswpin numbers are reduced to ~1/3. That means X desktop responsiveness is doubled under high memory/swap pressure. 1.2) test scenario - nfsroot gnome desktop with 512M physical memory - run some programs, and switch between the existing windows after starting each new program. 1.3) progress timing (seconds) before after programs 0.02 0.02 N xeyes 0.75 0.76 N firefox 2.02 1.88 N nautilus 3.36 3.17 N nautilus --browser 5.26 4.89 N gthumb 7.12 6.47 N gedit 9.22 8.16 N xpdf /usr/share/doc/shared-mime-info/shared-mime-info-spec.pdf 13.58 12.55 N xterm 15.87 14.57 N mlterm 18.63 17.06 N gnome-terminal 21.16 18.90 N urxvt 26.24 23.48 N gnome-system-monitor 28.72 26.52 N gnome-help 32.15 29.65 N gnome-dictionary 39.66 36.12 N /usr/games/sol 43.16 39.27 N /usr/games/gnometris 48.65 42.56 N /usr/games/gnect 53.31 47.03 N /usr/games/gtali 58.60 52.05 N /usr/games/iagno 65.77 55.42 N /usr/games/gnotravex 70.76 61.47 N /usr/games/mahjongg 76.15 67.11 N /usr/games/gnome-sudoku 86.32 75.15 N /usr/games/glines 92.21 79.70 N /usr/games/glchess 103.79 88.48 N /usr/games/gnomine 113.84 96.51 N /usr/games/gnotski 124.40 102.19 N /usr/games/gnibbles 137.41 114.93 N /usr/games/gnobots2 155.53 125.02 N /usr/games/blackjack 179.85 135.11 N /usr/games/same-gnome 224.49 154.50 N /usr/bin/gnome-window-properties 248.44 162.09 N /usr/bin/gnome-default-applications-properties 282.62 173.29 N /usr/bin/gnome-at-properties 323.72 188.21 N /usr/bin/gnome-typing-monitor 363.99 199.93 N /usr/bin/gnome-at-visual 394.21 206.95 N /usr/bin/gnome-sound-properties 435.14 224.49 N /usr/bin/gnome-at-mobility 463.05 234.11 N /usr/bin/gnome-keybinding-properties 503.75 248.59 N /usr/bin/gnome-about-me 554.00 276.27 N /usr/bin/gnome-display-properties 615.48 304.39 N /usr/bin/gnome-network-preferences 693.03 342.01 N /usr/bin/gnome-mouse-properties 759.90 388.58 N /usr/bin/gnome-appearance-properties 937.90 508.47 N /usr/bin/gnome-control-center 1109.75 587.57 N /usr/bin/gnome-keyboard-properties 1399.05 758.16 N : oocalc 1524.64 830.03 N : oodraw 1684.31 900.03 N : ooimpress 1874.04 993.91 N : oomath 2115.12 1081.89 N : ooweb 2369.02 1161.99 N : oowriter Note that the last ": oo*" commands are actually commented out. 1.4) vmstat numbers (some relevant ones are marked with *) before after nr_free_pages 1293 3898 nr_inactive_anon 59956 53460 nr_active_anon 26815 30026 nr_inactive_file 2657 3218 nr_active_file 2019 2806 nr_unevictable 4 4 nr_mlock 4 4 nr_anon_pages 26706 27859 *nr_mapped 3542 4469 nr_file_pages 72232 67681 nr_dirty 1 0 nr_writeback 123 19 nr_slab_reclaimable 3375 3534 nr_slab_unreclaimable 11405 10665 nr_page_table_pages 8106 7864 nr_unstable 0 0 nr_bounce 0 0 *nr_vmscan_write 394776 230839 nr_writeback_temp 0 0 numa_hit 6843353 3318676 numa_miss 0 0 numa_foreign 0 0 numa_interleave 1719 1719 numa_local 6843353 3318676 numa_other 0 0 *pgpgin 5954683 2057175 *pgpgout 1578276 922744 *pswpin 1486615 512238 *pswpout 394568 230685 pgalloc_dma 277432 56602 pgalloc_dma32 6769477 3310348 pgalloc_normal 0 0 pgalloc_movable 0 0 pgfree 7048396 3371118 pgactivate 2036343 1471492 pgdeactivate 2189691 1612829 pgfault 3702176 3100702 *pgmajfault 452116 201343 pgrefill_dma 12185 7127 pgrefill_dma32 334384 653703 pgrefill_normal 0 0 pgrefill_movable 0 0 pgsteal_dma 74214 22179 pgsteal_dma32 3334164 1638029 pgsteal_normal 0 0 pgsteal_movable 0 0 pgscan_kswapd_dma 1081421 1216199 pgscan_kswapd_dma32 58979118 46002810 pgscan_kswapd_normal 0 0 pgscan_kswapd_movable 0 0 pgscan_direct_dma 2015438 1086109 pgscan_direct_dma32 55787823 36101597 pgscan_direct_normal 0 0 pgscan_direct_movable 0 0 pginodesteal 3461 7281 slabs_scanned 564864 527616 kswapd_steal 2889797 1448082 kswapd_inodesteal 14827 14835 pageoutrun 43459 21562 allocstall 9653 4032 pgrotated 384216 228631 1.5) free numbers at the end of the tests before patch: total used free shared buffers cached Mem: 474 467 7 0 0 236 -/+ buffers/cache: 230 243 Swap: 1023 418 605 after patch: total used free shared buffers cached Mem: 474 457 16 0 0 236 -/+ buffers/cache: 221 253 Swap: 1023 404 619 2) memory flushing in a file server 2.1) brief summary The number of major faults from 50 to 3 during 10% cache hot reads. That means this patch successfully stops major faults when the active file list is slowly scanned when there are partially cache hot streaming IO. 2.2) test scenario Do 100000 pread(size=110 pages, offset=(i*100) pages), where 10% of the pages will be activated: for i in `seq 0 100 10000000`; do echo $i 110; done > pattern-hot-10 iotrace.rb --load pattern-hot-10 --play /b/sparse vmmon nr_mapped nr_active_file nr_inactive_file pgmajfault pgdeactivate pgfree and monitor /proc/vmstat during the time. The test box has 2G memory. I carried out tests on fresh booted console as well as X desktop, and fetched the vmstat numbers on (1) begin: shortly after the big read IO starts; (2) end: just before the big read IO stops; (3) restore: the big read IO stops and the zsh working set restored (4) restore X: after IO, switch back and forth between the urxvt and firefox windows to restore their working set. 2.3) console mode results nr_mapped nr_active_file nr_inactive_file pgmajfault pgdeactivate pgfree 2.6.29 VM_EXEC protection ON: begin: 2481 2237 8694 630 0 574299 end: 275 231976 233914 633 776271 20933042 restore: 370 232154 234524 691 777183 20958453 2.6.29 VM_EXEC protection ON (second run): begin: 2434 2237 8493 629 0 574195 end: 284 231970 233536 632 771918 20896129 restore: 399 232218 234789 690 774526 20957909 2.6.30-rc4-mm VM_EXEC protection OFF: begin: 2479 2344 9659 210 0 579643 end: 284 232010 234142 260 772776 20917184 restore: 379 232159 234371 301 774888 20967849 The above console numbers show that - The startup pgmajfault of 2.6.30-rc4-mm is merely 1/3 that of 2.6.29. I'd attribute that improvement to the mmap readahead improvements :-) - The pgmajfault increment during the file copy is 633-630=3 vs 260-210=50. That's a huge improvement - which means with the VM_EXEC protection logic, active mmap pages is pretty safe even under partially cache hot streaming IO. - when active:inactive file lru size reaches 1:1, their scan rates is 1:20.8 under 10% cache hot IO. (computed with formula Dpgdeactivate:Dpgfree) That roughly means the active mmap pages get 20.8 more chances to get re-referenced to stay in memory. - The absolute nr_mapped drops considerably to 1/9 during the big IO, and the dropped pages are mostly inactive ones. The patch has almost no impact in this aspect, that means it won't unnecessarily increase memory pressure. (In contrast, your 20% mmap protection ratio will keep them all, and therefore eliminate the extra 41 major faults to restore working set of zsh etc.) The iotrace.rb read throughput is 151.194384MB/s 284.198252s 100001x 450560b --load pattern-hot-10 --play /b/sparse which means the inactive list is rotated at the speed of 250MB/s, so a full scan of which takes about 3.5 seconds, while a full scan of active file list takes about 77 seconds. 2.4) X mode results We can reach roughly the same conclusions for X desktop: nr_mapped nr_active_file nr_inactive_file pgmajfault pgdeactivate pgfree 2.6.30-rc4-mm VM_EXEC protection ON: begin: 9740 8920 64075 561 0 678360 end: 768 218254 220029 565 798953 21057006 restore: 857 218543 220987 606 799462 21075710 restore X: 2414 218560 225344 797 799462 21080795 2.6.30-rc4-mm VM_EXEC protection OFF: begin: 9368 5035 26389 554 0 633391 end: 770 218449 221230 661 646472 17832500 restore: 1113 218466 220978 710 649881 17905235 restore X: 2687 218650 225484 947 802700 21083584 - the absolute nr_mapped drops considerably (to 1/13 of the original size) during the streaming IO. - the delta of pgmajfault is 3 vs 107 during IO, or 236 vs 393 during the whole process. Cc: Elladan <elladan@eskimo.com> Cc: Nick Piggin <npiggin@suse.de> Cc: Andi Kleen <andi@firstfloor.org> Cc: Christoph Lameter <cl@linux-foundation.org> Acked-by: Rik van Riel <riel@redhat.com> Acked-by: Peter Zijlstra <peterz@infradead.org> Acked-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Reviewed-by: Johannes Weiner <hannes@cmpxchg.org> Reviewed-by: Minchan Kim <minchan.kim@gmail.com> Signed-off-by: Wu Fengguang <fengguang.wu@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--mm/vmscan.c52
1 files changed, 45 insertions, 7 deletions
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 6be2068..1024979 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1212,6 +1212,7 @@ static void shrink_active_list(unsigned long nr_pages, struct zone *zone,
unsigned long pgscanned;
unsigned long vm_flags;
LIST_HEAD(l_hold); /* The pages which were snipped off */
+ LIST_HEAD(l_active);
LIST_HEAD(l_inactive);
struct page *page;
struct pagevec pvec;
@@ -1251,28 +1252,42 @@ static void shrink_active_list(unsigned long nr_pages, struct zone *zone,
/* page_referenced clears PageReferenced */
if (page_mapping_inuse(page) &&
- page_referenced(page, 0, sc->mem_cgroup, &vm_flags))
+ page_referenced(page, 0, sc->mem_cgroup, &vm_flags)) {
pgmoved++;
+ /*
+ * Identify referenced, file-backed active pages and
+ * give them one more trip around the active list. So
+ * that executable code get better chances to stay in
+ * memory under moderate memory pressure. Anon pages
+ * are not likely to be evicted by use-once streaming
+ * IO, plus JVM can create lots of anon VM_EXEC pages,
+ * so we ignore them here.
+ */
+ if ((vm_flags & VM_EXEC) && !PageAnon(page)) {
+ list_add(&page->lru, &l_active);
+ continue;
+ }
+ }
list_add(&page->lru, &l_inactive);
}
/*
- * Move the pages to the [file or anon] inactive list.
+ * Move pages back to the lru list.
*/
pagevec_init(&pvec, 1);
- lru = LRU_BASE + file * LRU_FILE;
spin_lock_irq(&zone->lru_lock);
/*
- * Count referenced pages from currently used mappings as
- * rotated, even though they are moved to the inactive list.
- * This helps balance scan pressure between file and anonymous
- * pages in get_scan_ratio.
+ * Count referenced pages from currently used mappings as rotated,
+ * even though only some of them are actually re-activated. This
+ * helps balance scan pressure between file and anonymous pages in
+ * get_scan_ratio.
*/
reclaim_stat->recent_rotated[!!file] += pgmoved;
pgmoved = 0; /* count pages moved to inactive list */
+ lru = LRU_BASE + file * LRU_FILE;
while (!list_empty(&l_inactive)) {
page = lru_to_page(&l_inactive);
prefetchw_prev_lru_page(page, &l_inactive, flags);
@@ -1295,6 +1310,29 @@ static void shrink_active_list(unsigned long nr_pages, struct zone *zone,
__mod_zone_page_state(zone, NR_LRU_BASE + lru, pgmoved);
__count_zone_vm_events(PGREFILL, zone, pgscanned);
__count_vm_events(PGDEACTIVATE, pgmoved);
+
+ pgmoved = 0; /* count pages moved back to active list */
+ lru = LRU_ACTIVE + file * LRU_FILE;
+ while (!list_empty(&l_active)) {
+ page = lru_to_page(&l_active);
+ prefetchw_prev_lru_page(page, &l_active, flags);
+ VM_BUG_ON(PageLRU(page));
+ SetPageLRU(page);
+ VM_BUG_ON(!PageActive(page));
+
+ list_move(&page->lru, &zone->lru[lru].list);
+ mem_cgroup_add_lru_list(page, lru);
+ pgmoved++;
+ if (!pagevec_add(&pvec, page)) {
+ spin_unlock_irq(&zone->lru_lock);
+ if (buffer_heads_over_limit)
+ pagevec_strip(&pvec);
+ __pagevec_release(&pvec);
+ spin_lock_irq(&zone->lru_lock);
+ }
+ }
+ __mod_zone_page_state(zone, NR_LRU_BASE + lru, pgmoved);
+
spin_unlock_irq(&zone->lru_lock);
if (buffer_heads_over_limit)
pagevec_strip(&pvec);