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Date: Tue, 18 Apr 2017 08:33:16 +0800
From: "Huang\, Ying" <ying.huang@...el.com>
To: Johannes Weiner <hannes@...xchg.org>
Cc: "Huang\, Ying" <ying.huang@...el.com>,
Andrew Morton <akpm@...ux-foundation.org>,
<linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
Andrea Arcangeli <aarcange@...hat.com>,
"Ebru Akagunduz" <ebru.akagunduz@...il.com>,
Michal Hocko <mhocko@...nel.org>, "Tejun Heo" <tj@...nel.org>,
Hugh Dickins <hughd@...gle.com>, Shaohua Li <shli@...nel.org>,
Minchan Kim <minchan@...nel.org>,
Rik van Riel <riel@...hat.com>, <cgroups@...r.kernel.org>
Subject: Re: [PATCH -mm -v8 1/3] mm, THP, swap: Delay splitting THP during swap out
Johannes Weiner <hannes@...xchg.org> writes:
> On Sat, Apr 15, 2017 at 09:17:04AM +0800, Huang, Ying wrote:
>> Hi, Johannes,
>>
>> Johannes Weiner <hannes@...xchg.org> writes:
>>
>> > Hi Huang,
>> >
>> > I reviewed this patch based on the feedback I already provided, but
>> > eventually gave up and rewrote it. Please take review feedback more
>> > seriously in the future.
>>
>> Thanks a lot for your help! I do respect all your review and effort.
>> The -v8 patch doesn't take all your comments, just because I thought we
>> have not reach consensus for some points and I want to use -v8 patch to
>> discuss them.
>>
>> One concern I have before is whether to split THP firstly when swap
>> space or memcg swap is used up. Now I think your solution is
>> acceptable. And if we receive any regression report for that in the
>> future, it's not very hard to deal with.
>
> If you look at get_scan_count(), we'll stop scanning anonymous pages
> altogether when swap space runs out. So it might happen to a few THP,
> but it shouldn't be a big deal.
Yes. It only influences a few THP.
> And yes, in that case I'd really rather wait for any real problems to
> materialize before we complicate things.
>
>> > Attached below is the reworked patch. Most changes are to the layering
>> > (page functions, cluster functions, range functions) so that we don't
>> > make the lowest swap range code require a notion of huge pages, or
>> > make the memcg page functions take size information that can be
>> > gathered from the page itself. I turned the config symbol into a
>> > generic THP_SWAP that can later be extended when we add 2MB IO. The
>> > rest is function naming, #ifdef removal etc.
>>
>> For some #ifdef in swapfile.c, it is to avoid unnecessary code size
>> increase for !CONFIG_TRANSPARENT_HUGEPAGE or platform with THP swap
>> optimization disabled. Is it an issue?
>
> It saves some code size, but it looks like the biggest cost comes from
> bloating PageSwapCache(). This is mm/builtin.o with !CONFIG_THP:
>
> add/remove: 1/0 grow/shrink: 34/5 up/down: 920/-311 (609)
> function old new delta
> __free_cluster - 106 +106
> get_swap_pages 465 555 +90
> migrate_page_move_mapping 1404 1479 +75
> shrink_page_list 3573 3632 +59
> __delete_from_swap_cache 235 293 +58
> __test_set_page_writeback 626 678 +52
> __swap_writepage 766 812 +46
> try_to_unuse 1763 1795 +32
> madvise_free_pte_range 882 912 +30
> __set_page_dirty_nobuffers 245 268 +23
> migrate_page_copy 565 587 +22
> swap_slot_free_notify 133 151 +18
> shmem_replace_page 616 633 +17
> try_to_free_swap 135 151 +16
> test_clear_page_writeback 512 528 +16
> swap_set_page_dirty 109 125 +16
> swap_readpage 384 400 +16
> shmem_unuse 1535 1551 +16
> reuse_swap_page 340 356 +16
> page_mapping 144 160 +16
> migrate_huge_page_move_mapping 483 499 +16
> free_swap_and_cache 409 425 +16
> free_pages_and_swap_cache 161 177 +16
> free_page_and_swap_cache 145 161 +16
> do_swap_page 1216 1232 +16
> __remove_mapping 408 424 +16
> __page_file_mapping 82 98 +16
> __page_file_index 70 85 +15
> try_to_unmap_one 1324 1337 +13
> shmem_getpage_gfp.isra 2358 2371 +13
> add_to_swap_cache 47 60 +13
> inc_cluster_info_page 204 210 +6
> get_swap_page 411 415 +4
> shmem_writepage 922 925 +3
> sys_swapon 4210 4211 +1
> swapcache_free_entries 786 768 -18
> __add_to_swap_cache 445 406 -39
> delete_from_swap_cache 149 104 -45
> scan_swap_map_slots 1953 1889 -64
> swap_do_scheduled_discard 713 568 -145
> Total: Before=454535, After=455144, chg +0.13%
>
> If I make the compound_head() in there conditional, this patch
> actually ends up shrinking the code due to the refactoring of the
> cluster functions:
>
> add/remove: 1/0 grow/shrink: 10/5 up/down: 302/-327 (-25)
> function old new delta
> __free_cluster - 106 +106
> get_swap_pages 465 555 +90
> __delete_from_swap_cache 235 277 +42
> shmem_replace_page 616 633 +17
> migrate_page_move_mapping 1404 1418 +14
> add_to_swap_cache 47 60 +13
> migrate_page_copy 565 571 +6
> inc_cluster_info_page 204 210 +6
> get_swap_page 411 415 +4
> shmem_writepage 922 925 +3
> sys_swapon 4210 4211 +1
> swapcache_free_entries 786 768 -18
> delete_from_swap_cache 149 104 -45
> __add_to_swap_cache 445 390 -55
> scan_swap_map_slots 1953 1889 -64
> swap_do_scheduled_discard 713 568 -145
> Total: Before=454535, After=454510, chg -0.01%
This looks great! Thanks!
> But PageSwapCache() is somewhat ugly either way. Even with THP_SWAP
> compiled in, it seems like most callsites wouldn't test tailpages?
> Can we get rid of the compound_head() and annotate any callsites
> working on potential tail pages?
I think we can keep the current #ifdef version and make some cleanup in
the next step?
>> > Please review whether this is an acceptable version for you.
>>
>> Yes. It is good for me. I will give it more test on next Monday.
>
> Thanks
I think we will fold the below patch into the original one?
Best Regards,
Huang, Ying
> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> index f4acd6c4f808..d33e3280c8ad 100644
> --- a/include/linux/page-flags.h
> +++ b/include/linux/page-flags.h
> @@ -326,7 +326,9 @@ PAGEFLAG_FALSE(HighMem)
> #ifdef CONFIG_SWAP
> static __always_inline int PageSwapCache(struct page *page)
> {
> +#ifdef CONFIG_THP_SWAP
> page = compound_head(page);
> +#endif
> return PageSwapBacked(page) && test_bit(PG_swapcache, &page->flags);
>
> }
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index 34adac6e9457..a4dba6975e7b 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -401,7 +401,6 @@ extern int swap_duplicate(swp_entry_t);
> extern int swapcache_prepare(swp_entry_t);
> extern void swap_free(swp_entry_t);
> extern void swapcache_free(swp_entry_t);
> -extern void swapcache_free_cluster(swp_entry_t);
> extern void swapcache_free_entries(swp_entry_t *entries, int n);
> extern int free_swap_and_cache(swp_entry_t);
> extern int swap_type_of(dev_t, sector_t, struct block_device **);
> @@ -467,10 +466,6 @@ static inline void swapcache_free(swp_entry_t swp)
> {
> }
>
> -static inline void swapcache_free_cluster(swp_entry_t swp)
> -{
> -}
> -
> static inline struct page *swapin_readahead(swp_entry_t swp, gfp_t gfp_mask,
> struct vm_area_struct *vma, unsigned long addr)
> {
> @@ -592,5 +587,13 @@ static inline bool mem_cgroup_swap_full(struct page *page)
> }
> #endif
>
> +#ifdef CONFIG_THP_SWAP
> +extern void swapcache_free_cluster(swp_entry_t);
> +#else
> +static inline void swapcache_free_cluster(swp_entry_t swp)
> +{
> +}
> +#endif
> +
> #endif /* __KERNEL__*/
> #endif /* _LINUX_SWAP_H */
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index f597cabcaab7..eeaf145b2a20 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -825,6 +825,7 @@ static int scan_swap_map_slots(struct swap_info_struct *si,
> return n_ret;
> }
>
> +#ifdef CONFIG_THP_SWAP
> static int swap_alloc_cluster(struct swap_info_struct *si, swp_entry_t *slot)
> {
> unsigned long idx;
> @@ -862,6 +863,13 @@ static void swap_free_cluster(struct swap_info_struct *si, unsigned long idx)
> unlock_cluster(ci);
> swap_range_free(si, offset, SWAPFILE_CLUSTER);
> }
> +#else
> +static int swap_alloc_cluster(struct swap_info_struct *si, swp_entry_t *slot)
> +{
> + VM_WARN_ON_ONCE(1);
> + return 0;
> +}
> +#endif /* CONFIG_THP_SWAP */
>
> static unsigned long scan_swap_map(struct swap_info_struct *si,
> unsigned char usage)
> @@ -1145,6 +1153,7 @@ void swapcache_free(swp_entry_t entry)
> }
> }
>
> +#ifdef CONFIG_THP_SWAP
> void swapcache_free_cluster(swp_entry_t entry)
> {
> unsigned long offset = swp_offset(entry);
> @@ -1170,6 +1179,7 @@ void swapcache_free_cluster(swp_entry_t entry)
> swap_free_cluster(si, idx);
> spin_unlock(&si->lock);
> }
> +#endif /* CONFIG_THP_SWAP */
>
> void swapcache_free_entries(swp_entry_t *entries, int n)
> {
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