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Date: Wed, 15 Mar 2017 09:08:46 +0800
From: "Huang\, Ying" <ying.huang@...el.com>
To: Tim Chen <tim.c.chen@...ux.intel.com>
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>,
"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
Hugh Dickins <hughd@...gle.com>,
"Shaohua Li" <shli@...nel.org>, Minchan Kim <minchan@...nel.org>,
Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH -mm -v6 4/9] mm, THP, swap: Add get_huge_swap_page()
Tim Chen <tim.c.chen@...ux.intel.com> writes:
> On Wed, 2017-03-08 at 15:26 +0800, Huang, Ying wrote:
>> From: Huang Ying <ying.huang@...el.com>
>>
>> A variation of get_swap_page(), get_huge_swap_page(), is added to
>> allocate a swap cluster (HPAGE_PMD_NR swap slots) based on the swap
>> cluster allocation function. A fair simple algorithm is used, that is,
>> only the first swap device in priority list will be tried to allocate
>> the swap cluster. The function will fail if the trying is not
>> successful, and the caller will fallback to allocate a single swap slot
>> instead. This works good enough for normal cases.
>>
>> This will be used for the THP (Transparent Huge Page) swap support.
>> Where get_huge_swap_page() will be used to allocate one swap cluster for
>> each THP swapped out.
>>
>> Because of the algorithm adopted, if the difference of the number of the
>> free swap clusters among multiple swap devices is significant, it is
>> possible that some THPs are split earlier than necessary. For example,
>> this could be caused by big size difference among multiple swap devices.
>>
>> Cc: Andrea Arcangeli <aarcange@...hat.com>
>> Cc: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
>> Cc: Hugh Dickins <hughd@...gle.com>
>> Cc: Shaohua Li <shli@...nel.org>
>> Cc: Minchan Kim <minchan@...nel.org>
>> Cc: Rik van Riel <riel@...hat.com>
>> Signed-off-by: "Huang, Ying" <ying.huang@...el.com>
>> ---
>> include/linux/swap.h | 19 ++++++++++++++++++-
>> mm/swap_slots.c | 5 +++--
>> mm/swapfile.c | 16 ++++++++++++----
>> 3 files changed, 33 insertions(+), 7 deletions(-)
>>
>> diff --git a/include/linux/swap.h b/include/linux/swap.h
>> index 278e1349a424..e3a7609a8989 100644
>> --- a/include/linux/swap.h
>> +++ b/include/linux/swap.h
>> @@ -388,7 +388,7 @@ static inline long get_nr_swap_pages(void)
>> extern void si_swapinfo(struct sysinfo *);
>> extern swp_entry_t get_swap_page(void);
>> extern swp_entry_t get_swap_page_of_type(int);
>> -extern int get_swap_pages(int n, swp_entry_t swp_entries[]);
>> +extern int get_swap_pages(int n, swp_entry_t swp_entries[], bool huge);
>> extern int add_swap_count_continuation(swp_entry_t, gfp_t);
>> extern void swap_shmem_alloc(swp_entry_t);
>> extern int swap_duplicate(swp_entry_t);
>> @@ -527,6 +527,23 @@ static inline swp_entry_t get_swap_page(void)
>>
>> #endif /* CONFIG_SWAP */
>>
>> +#ifdef CONFIG_THP_SWAP_CLUSTER
>> +static inline swp_entry_t get_huge_swap_page(void)
>> +{
>> + swp_entry_t entry;
>> +
>> + if (get_swap_pages(1, &entry, true))
>> + return entry;
>> + else
>> + return (swp_entry_t) {0};
>> +}
>> +#else
>> +static inline swp_entry_t get_huge_swap_page(void)
>> +{
>> + return (swp_entry_t) {0};
>> +}
>> +#endif
>> +
>> #ifdef CONFIG_MEMCG
>> static inline int mem_cgroup_swappiness(struct mem_cgroup *memcg)
>> {
>> diff --git a/mm/swap_slots.c b/mm/swap_slots.c
>> index 9b5bc86f96ad..075bb39e03c5 100644
>> --- a/mm/swap_slots.c
>> +++ b/mm/swap_slots.c
>> @@ -258,7 +258,8 @@ static int refill_swap_slots_cache(struct swap_slots_cache *cache)
>>
>> cache->cur = 0;
>> if (swap_slot_cache_active)
>> - cache->nr = get_swap_pages(SWAP_SLOTS_CACHE_SIZE, cache->slots);
>> + cache->nr = get_swap_pages(SWAP_SLOTS_CACHE_SIZE, cache->slots,
>> + false);
>>
>> return cache->nr;
>> }
>> @@ -334,7 +335,7 @@ swp_entry_t get_swap_page(void)
>> return entry;
>> }
>>
>> - get_swap_pages(1, &entry);
>> + get_swap_pages(1, &entry, false);
>>
>> return entry;
>> }
>> diff --git a/mm/swapfile.c b/mm/swapfile.c
>> index 91876c33114b..7241c937e52b 100644
>> --- a/mm/swapfile.c
>> +++ b/mm/swapfile.c
>> @@ -904,11 +904,12 @@ static unsigned long scan_swap_map(struct swap_info_struct *si,
>>
>> }
>>
>> -int get_swap_pages(int n_goal, swp_entry_t swp_entries[])
>
>
>> +int get_swap_pages(int n_goal, swp_entry_t swp_entries[], bool huge)
>> {
>> struct swap_info_struct *si, *next;
>> long avail_pgs;
>> int n_ret = 0;
>> + int nr_pages = huge_cluster_nr_entries(huge);
>>
>> avail_pgs = atomic_long_read(&nr_swap_pages);
>> if (avail_pgs <= 0)
>> @@ -920,6 +921,10 @@ int get_swap_pages(int n_goal, swp_entry_t swp_entries[])
>> if (n_goal > avail_pgs)
>> n_goal = avail_pgs;
>>
>> + n_goal *= nr_pages;
>
> I think if (n_goal > 1) when huge is true,
> n_goal should be set to huge_cluster_nr_entries(huge) here
> or we could have an invalid check below. We probably
> should add a comment to get_swap_pages on how we treat
> n_goal when huge is true. Maybe say we will always treat
> n_goal as SWAPFILE_CLUSTER when huge is true.
Yes. The meaning of n_goal and n_ret isn't consistent between huge and
normal swap entry allocation. I will revise the logic in the function
to make them consistent.
>> + if (avail_pgs < n_goal)
>> + goto noswap;
>> +
>> atomic_long_sub(n_goal, &nr_swap_pages);
>>
>> spin_lock(&swap_avail_lock);
>> @@ -946,10 +951,13 @@ int get_swap_pages(int n_goal, swp_entry_t swp_entries[])
>> spin_unlock(&si->lock);
>> goto nextsi;
>> }
>> - n_ret = scan_swap_map_slots(si, SWAP_HAS_CACHE,
>> - n_goal, swp_entries);
>> + if (likely(nr_pages == 1))
>
> if (likely(!huge)) is probably more readable
Sure.
Best Regards,
Huang, Ying
>> + n_ret = scan_swap_map_slots(si, SWAP_HAS_CACHE,
>> + n_goal, swp_entries);
>> + else
>> + n_ret = swap_alloc_huge_cluster(si, swp_entries);
>> spin_unlock(&si->lock);
>
> Thanks.
>
> Tim
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