linux-kernel - Re: [PATCH -mm -v6 3/9] mm, THP, swap: Add swap cluster allocate/free functions

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Date:   Wed, 15 Mar 2017 09:19:27 +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 3/9] mm, THP, swap: Add swap cluster allocate/free functions

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>
>> 
>> The swap cluster allocation/free functions are added based on the
>> existing swap cluster management mechanism for SSD.  These functions
>> don't work for the rotating hard disks because the existing swap cluster
>> management mechanism doesn't work for them.  The hard disks support may
>> be added if someone really need it.  But that needn't be included in
>> this patchset.
>> 
>> This will be used for the THP (Transparent Huge Page) swap support.
>> Where one swap cluster will hold the contents of each THP swapped out.
>> 
>> 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>
>> ---
>>  mm/swapfile.c | 217 +++++++++++++++++++++++++++++++++++++++++-----------------
>>  1 file changed, 156 insertions(+), 61 deletions(-)
>> 
>> diff --git a/mm/swapfile.c b/mm/swapfile.c
>> index a744604384ff..91876c33114b 100644
>> --- a/mm/swapfile.c
>> +++ b/mm/swapfile.c
>> @@ -378,6 +378,14 @@ static void swap_cluster_schedule_discard(struct swap_info_struct *si,
>>  	schedule_work(&si->discard_work);
>>  }
>>  
>> +static void __free_cluster(struct swap_info_struct *si, unsigned long idx)
>> +{
>> +	struct swap_cluster_info *ci = si->cluster_info;
>> +
>> +	cluster_set_flag(ci + idx, CLUSTER_FLAG_FREE);
>> +	cluster_list_add_tail(&si->free_clusters, ci, idx);
>> +}
>> +
>>  /*
>>   * Doing discard actually. After a cluster discard is finished, the cluster
>>   * will be added to free cluster list. caller should hold si->lock.
>> @@ -398,10 +406,7 @@ static void swap_do_scheduled_discard(struct swap_info_struct *si)
>>  
>>  		spin_lock(&si->lock);
>>  		ci = lock_cluster(si, idx * SWAPFILE_CLUSTER);
>> -		cluster_set_flag(ci, CLUSTER_FLAG_FREE);
>> -		unlock_cluster(ci);
>> -		cluster_list_add_tail(&si->free_clusters, info, idx);
>> -		ci = lock_cluster(si, idx * SWAPFILE_CLUSTER);
>> +		__free_cluster(si, idx);
>>  		memset(si->swap_map + idx * SWAPFILE_CLUSTER,
>>  				0, SWAPFILE_CLUSTER);
>>  		unlock_cluster(ci);
>
> The __free_cluster definition and the above change to eliminate
> the extra unlock_cluster and lock_cluster can perhaps be broken up
> as a separate patch.  It can be independent of THP changes.

I think the change may have no value by itself without THP changes.
There will be only 1 user of __free_cluster() and the lock change is
trivial too.  So I think it may be better just to keep it as that?

Best Regards,
Huang, Ying