linux-kernel - Re: [PATCH -V2 3/5] swap: remove __swp

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Date:   Tue, 23 May 2023 08:50:24 +0800
From:   "Huang, Ying" <ying.huang@...el.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Hugh Dickins <hughd@...gle.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Matthew Wilcox <willy@...radead.org>,
        Michal Hocko <mhocko@...e.com>,
        Minchan Kim <minchan@...nel.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Yang Shi <shy828301@...il.com>, Yu Zhao <yuzhao@...gle.com>
Subject: Re: [PATCH -V2 3/5] swap: remove __swp_swapcount()

David Hildenbrand <david@...hat.com> writes:

> On 22.05.23 09:09, Huang Ying wrote:
>> __swp_swapcount() just encloses the calling to swap_swapcount() with
>> get/put_swap_device().  It is called in __read_swap_cache_async()
>> only, which encloses the calling with get/put_swap_device() already.
>> So, __read_swap_cache_async() can call swap_swapcount() directly.
>
> The previous patch contained the hunk
>
> -		if (!__swp_swapcount(entry) && swap_slot_cache_enabled)
> -			return NULL;
> +		if (!swap_swapcount(si, entry) && swap_slot_cache_enabled)
> +			goto fail;
>  
> So something is a bit off here. Either that hunk should go here, or
> this patch description has to be adjusted.
>
>
> But I guess patch #2 doesn't compile on its own because this patch
> here adds swap_swapcount() to include/linux/swap.h ?

Good catch!  Will change this in the next version.

Best Regards,
Huang, Ying

>> Signed-off-by: "Huang, Ying" <ying.huang@...el.com>
>> Cc: David Hildenbrand <david@...hat.com>
>> Cc: Hugh Dickins <hughd@...gle.com>
>> Cc: Johannes Weiner <hannes@...xchg.org>
>> Cc: Matthew Wilcox <willy@...radead.org>
>> Cc: Michal Hocko <mhocko@...e.com>
>> Cc: Minchan Kim <minchan@...nel.org>
>> Cc: Tim Chen <tim.c.chen@...ux.intel.com>
>> Cc: Yang Shi <shy828301@...il.com>
>> Cc: Yu Zhao <yuzhao@...gle.com>
>> ---
>>   include/linux/swap.h |  4 ++--
>>   mm/swapfile.c        | 20 +-------------------
>>   2 files changed, 3 insertions(+), 21 deletions(-)
>> diff --git a/include/linux/swap.h b/include/linux/swap.h
>> index 3c69cb653cb9..f6bd51aa05ea 100644
>> --- a/include/linux/swap.h
>> +++ b/include/linux/swap.h
>> @@ -512,7 +512,7 @@ int find_first_swap(dev_t *device);
>>   extern unsigned int count_swap_pages(int, int);
>>   extern sector_t swapdev_block(int, pgoff_t);
>>   extern int __swap_count(swp_entry_t entry);
>> -extern int __swp_swapcount(swp_entry_t entry);
>> +extern int swap_swapcount(struct swap_info_struct *si, swp_entry_t entry);
>>   extern int swp_swapcount(swp_entry_t entry);
>>   extern struct swap_info_struct *page_swap_info(struct page *);
>>   extern struct swap_info_struct *swp_swap_info(swp_entry_t entry);
>> @@ -590,7 +590,7 @@ static inline int __swap_count(swp_entry_t entry)
>>   	return 0;
>>   }
>>   -static inline int __swp_swapcount(swp_entry_t entry)
>> +static inline int swap_swapcount(struct swap_info_struct *si, swp_entry_t entry)
>>   {
>>   	return 0;
>>   }
>> diff --git a/mm/swapfile.c b/mm/swapfile.c
>> index 8419cba9c192..e9cce775fb25 100644
>> --- a/mm/swapfile.c
>> +++ b/mm/swapfile.c
>> @@ -1443,7 +1443,7 @@ int __swap_count(swp_entry_t entry)
>>    * This does not give an exact answer when swap count is continued,
>>    * but does include the high COUNT_CONTINUED flag to allow for that.
>>    */
>> -static int swap_swapcount(struct swap_info_struct *si, swp_entry_t entry)
>> +int swap_swapcount(struct swap_info_struct *si, swp_entry_t entry)
>>   {
>>   	pgoff_t offset = swp_offset(entry);
>>   	struct swap_cluster_info *ci;
>> @@ -1455,24 +1455,6 @@ static int swap_swapcount(struct swap_info_struct *si, swp_entry_t entry)
>>   	return count;
>>   }
>>   -/*
>> - * How many references to @entry are currently swapped out?
>> - * This does not give an exact answer when swap count is continued,
>> - * but does include the high COUNT_CONTINUED flag to allow for that.
>> - */
>> -int __swp_swapcount(swp_entry_t entry)
>> -{
>> -	int count = 0;
>> -	struct swap_info_struct *si;
>> -
>> -	si = get_swap_device(entry);
>> -	if (si) {
>> -		count = swap_swapcount(si, entry);
>> -		put_swap_device(si);
>> -	}
>> -	return count;
>> -}
>> -
>>   /*
>>    * How many references to @entry are currently swapped out?
>>    * This considers COUNT_CONTINUED so it returns exact answer.