Re: [PATCH v2 03/10] mm: don't pass "enum lru_list" to lru list addition functions
From: Alex Shi
Date: Wed Feb 24 2021 - 03:07:42 EST
在 2021/2/24 下午1:29, Yu Zhao 写道:
> On Tue, Feb 23, 2021 at 02:50:11PM -0800, Andrew Morton wrote:
>> On Tue, 26 Jan 2021 15:14:38 -0700 Yu Zhao <yuzhao@xxxxxxxxxx> wrote:
>>
>>> On Tue, Jan 26, 2021 at 10:01:11PM +0000, Matthew Wilcox wrote:
>>>> On Fri, Jan 22, 2021 at 03:05:53PM -0700, Yu Zhao wrote:
>>>>> +++ b/mm/swap.c
>>>>> @@ -231,7 +231,7 @@ static void pagevec_move_tail_fn(struct page *page, struct lruvec *lruvec)
>>>>> if (!PageUnevictable(page)) {
>>>>> del_page_from_lru_list(page, lruvec, page_lru(page));
>>>>> ClearPageActive(page);
>>>>> - add_page_to_lru_list_tail(page, lruvec, page_lru(page));
>>>>> + add_page_to_lru_list_tail(page, lruvec);
>>>>> __count_vm_events(PGROTATED, thp_nr_pages(page));
>>>>> }
>>>>
>>>> Is it profitable to do ...
>>>>
>>>> - del_page_from_lru_list(page, lruvec, page_lru(page));
>>>> + enum lru_list lru = page_lru(page);
>>>> + del_page_from_lru_list(page, lruvec, lru);
>>>> ClearPageActive(page);
>>>> - add_page_to_lru_list_tail(page, lruvec, page_lru(page));
>>>> + lru &= ~LRU_ACTIVE;
>>>> + add_page_to_lru_list_tail(page, lruvec, lru);
>>>
>>> Ok, now we want to trade readability for size. Sure, I'll see how
>>> much we could squeeze.
>>
>> As nothing has happened here and the code bloat issue remains, I'll
>> hold this series out of 5.12-rc1.
>
> Sorry for the slow response. I was trying to ascertain why
> page_lru(), a tiny helper, could bloat vmlinux by O(KB). It turned out
> compound_head() included in Page{Active,Unevictable} is a nuisance in
> our case. Testing PG_{active,unevictable} against
> compound_head(page)->flags is really unnecessary because all lru
> operations are eventually done on page->lru not
> compound_head(page)->lru. With the following change, which sacrifices
> the readability a bit, we gain 998 bytes with Clang but lose 227 bytes
> with GCC, which IMO is a win. (We use Clang by default.)
>
>
> diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h
> index 355ea1ee32bd..ec0878a3cdfe 100644
> --- a/include/linux/mm_inline.h
> +++ b/include/linux/mm_inline.h
> @@ -46,14 +46,12 @@ static __always_inline void __clear_page_lru_flags(struct page *page)
> {
> VM_BUG_ON_PAGE(!PageLRU(page), page);
>
> - __ClearPageLRU(page);
> -
> /* this shouldn't happen, so leave the flags to bad_page() */
> - if (PageActive(page) && PageUnevictable(page))
> + if ((page->flags & (BIT(PG_active) | BIT(PG_unevictable))) ==
> + (BIT(PG_active) | BIT(PG_unevictable)))
> return;
>
> - __ClearPageActive(page);
> - __ClearPageUnevictable(page);
> + page->flags &= ~(BIT(PG_lru) | BIT(PG_active) | BIT(PG_unevictable));
> }
>
> /**
> @@ -65,18 +63,12 @@ static __always_inline void __clear_page_lru_flags(struct page *page)
> */
> static __always_inline enum lru_list page_lru(struct page *page)
> {
> - enum lru_list lru;
> + unsigned long flags = READ_ONCE(page->flags);
>
> VM_BUG_ON_PAGE(PageActive(page) && PageUnevictable(page), page);
>
> - if (PageUnevictable(page))
> - return LRU_UNEVICTABLE;
> -
> - lru = page_is_file_lru(page) ? LRU_INACTIVE_FILE : LRU_INACTIVE_ANON;
> - if (PageActive(page))
> - lru += LRU_ACTIVE;
> -
> - return lru;
> + return (flags & BIT(PG_unevictable)) ? LRU_UNEVICTABLE :
> + (LRU_FILE * !(flags & BIT(PG_swapbacked)) + !!(flags & BIT(PG_active)));
Currently each of page flags used different flags policy, does this mean above flags could be
change to PF_ANY policy?
Thanks
Alex
> }
>
> static __always_inline void add_page_to_lru_list(struct page *page,
>
>
> I'll post this as a separate patch. Below the bloat-o-meter collected
> on top of c03c21ba6f4e.
>
> $ ./scripts/bloat-o-meter ../vmlinux.clang.orig ../vmlinux.clang
> add/remove: 0/1 grow/shrink: 7/10 up/down: 191/-1189 (-998)
> Function old new delta
> lru_lazyfree_fn 848 893 +45
> lru_deactivate_file_fn 1037 1075 +38
> perf_trace_mm_lru_insertion 515 548 +33
> check_move_unevictable_pages 983 1006 +23
> __activate_page 706 729 +23
> trace_event_raw_event_mm_lru_insertion 476 497 +21
> lru_deactivate_fn 691 699 +8
> __bpf_trace_mm_lru_insertion 13 11 -2
> __traceiter_mm_lru_insertion 67 62 -5
> move_pages_to_lru 964 881 -83
> __pagevec_lru_add_fn 665 581 -84
> isolate_lru_page 524 419 -105
> __munlock_pagevec 1609 1481 -128
> isolate_migratepages_block 3370 3237 -133
> __page_cache_release 556 413 -143
> lruvec_lru_size 151 - -151
> release_pages 1025 866 -159
> pagevec_move_tail_fn 805 609 -196
> Total: Before=19502982, After=19501984, chg -0.01%
>
> $ ./scripts/bloat-o-meter ../vmlinux.gcc.orig ../vmlinux.gcc
> add/remove: 0/1 grow/shrink: 9/9 up/down: 1010/-783 (227)
> Function old new delta
> shrink_lruvec 1690 1950 +260
> lru_deactivate_file_fn 961 1128 +167
> isolate_migratepages_block 3286 3427 +141
> check_move_unevictable_pages 1042 1170 +128
> lru_lazyfree_fn 709 822 +113
> lru_deactivate_fn 665 724 +59
> __activate_page 703 760 +57
> trace_event_raw_event_mm_lru_insertion 432 478 +46
> perf_trace_mm_lru_insertion 464 503 +39
> __bpf_trace_mm_lru_insertion 13 11 -2
> __traceiter_mm_lru_insertion 66 57 -9
> isolate_lru_page 472 405 -67
> __munlock_pagevec 1282 1212 -70
> __pagevec_lru_add 976 893 -83
> __page_cache_release 508 418 -90
> release_pages 978 887 -91
> move_pages_to_lru 954 853 -101
> lruvec_lru_size 131 - -131
> pagevec_move_tail_fn 770 631 -139
> Total: Before=19237248, After=19237475, chg +0.00%
>