On 19.04.21 12:14, Mike Rapoport wrote:
On Mon, Apr 19, 2021 at 11:40:56AM +0200, David Hildenbrand wrote:
On 19.04.21 11:38, David Hildenbrand wrote:
On 19.04.21 11:36, Mike Rapoport wrote:
On Mon, Apr 19, 2021 at 11:15:02AM +0200, David Hildenbrand wrote:
On 19.04.21 10:42, Mike Rapoport wrote:
From: Mike Rapoport rppt@linux.ibm.com
Kernel test robot reported -4.2% regression of will-it-scale.per_thread_ops due to commit "mm: introduce memfd_secret system call to create "secret" memory areas".
The perf profile of the test indicated that the regression is caused by page_is_secretmem() called from gup_pte_range() (inlined by gup_pgd_range):
27.76 +2.5 30.23 perf-profile.children.cycles-pp.gup_pgd_range 0.00 +3.2 3.19 ± 2% perf-profile.children.cycles-pp.page_mapping 0.00 +3.7 3.66 ± 2% perf-profile.children.cycles-pp.page_is_secretmemFurther analysis showed that the slow down happens because neither page_is_secretmem() nor page_mapping() are not inline and moreover, multiple page flags checks in page_mapping() involve calling compound_head() several times for the same page.
Make page_is_secretmem() inline and replace page_mapping() with page flag checks that do not imply page-to-head conversion.
Reported-by: kernel test robot oliver.sang@intel.com Signed-off-by: Mike Rapoport rppt@linux.ibm.com
@Andrew, The patch is vs v5.12-rc7-mmots-2021-04-15-16-28, I'd appreciate if it would be added as a fixup to the memfd_secret series.
include/linux/secretmem.h | 26 +++++++++++++++++++++++++- mm/secretmem.c | 12 +----------- 2 files changed, 26 insertions(+), 12 deletions(-)diff --git a/include/linux/secretmem.h b/include/linux/secretmem.h index 907a6734059c..b842b38cbeb1 100644 --- a/include/linux/secretmem.h +++ b/include/linux/secretmem.h @@ -4,8 +4,32 @@ #ifdef CONFIG_SECRETMEM +extern const struct address_space_operations secretmem_aops;
+static inline bool page_is_secretmem(struct page *page) +{
- struct address_space *mapping;
- /*
* Using page_mapping() is quite slow because of the actual call* instruction and repeated compound_head(page) inside the* page_mapping() function.* We know that secretmem pages are not compound and LRU so we can* save a couple of cycles here.*/- if (PageCompound(page) || !PageLRU(page))
return false;I'd assume secretmem pages are rare in basically every setup out there. So maybe throwing in a couple of likely()/unlikely() might make sense.
I'd say we could do unlikely(page_is_secretmem()) at call sites. Here I can hardly estimate which pages are going to be checked.
- mapping = (struct address_space *)
((unsigned long)page->mapping & ~PAGE_MAPPING_FLAGS);Not sure if open-coding page_mapping is really a good idea here -- or even necessary after the fast path above is in place. Anyhow, just my 2 cents.
Well, most if the -4.2% of the performance regression kbuild reported were due to repeated compount_head(page) in page_mapping(). So the whole point of this patch is to avoid calling page_mapping().
I would have thought the fast path "(PageCompound(page) || !PageLRU(page))" would already avoid calling page_mapping() in many cases.
(and I do wonder if a generic page_mapping() optimization would make sense instead)
Not sure. Replacing page_mapping() with page_file_mapping() at the call sites at fs/ and mm/ increased the defconfig image by nearly 2k and page_file_mapping() is way simpler than page_mapping()
add/remove: 1/0 grow/shrink: 35/0 up/down: 1960/0 (1960) Function old new delta shrink_page_list 3414 3670 +256 __set_page_dirty_nobuffers 242 349 +107 check_move_unevictable_pages 904 987 +83 move_to_new_page 591 671 +80 shrink_active_list 912 970 +58 move_pages_to_lru 911 965 +54 migrate_pages 2500 2554 +54 shmem_swapin_page 1145 1197 +52 shmem_undo_range 1669 1719 +50 __test_set_page_writeback 620 670 +50 __set_page_dirty_buffers 187 237 +50 __pagevec_lru_add 757 807 +50 __munlock_pagevec 1155 1205 +50 __dump_page 1101 1151 +50 __cancel_dirty_page 182 232 +50 __remove_mapping 461 510 +49 rmap_walk_file 402 449 +47 isolate_movable_page 240 287 +47 test_clear_page_writeback 668 714 +46 page_cache_pipe_buf_try_steal 171 217 +46 page_endio 246 290 +44 page_file_mapping - 43 +43 __isolate_lru_page_prepare 254 297 +43 hugetlb_page_mapping_lock_write 39 81 +42 iomap_set_page_dirty 110 151 +41 clear_page_dirty_for_io 324 364 +40 wait_on_page_writeback_killable 118 157 +39 wait_on_page_writeback 105 144 +39 set_page_dirty 159 198 +39 putback_movable_page 32 71 +39 page_mkclean 172 211 +39 mark_buffer_dirty 176 215 +39 invalidate_inode_page 122 161 +39 delete_from_page_cache 139 178 +39 PageMovable 49 86 +37 isolate_migratepages_block 2843 2872 +29 Total: Before=17068648, After=17070608, chg +0.01%
Willy can most probably give the best advise here :)
I think that's what folios are for :)
Exactly my thought. :)