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Subject: Re: [PATCH] mm: thp: don't need drain lru cache when splitting and
 mlocking THP
To:     Daniel Jordan <daniel.m.jordan@oracle.com>
Cc:     kirill.shutemov@linux.intel.com, hughd@google.com,
        aarcange@redhat.com, akpm@linux-foundation.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
References: <1585337380-97368-1-git-send-email-yang.shi@linux.alibaba.com>
 <20200402230411.7ckwkmd6wwtqfkm2@ca-dmjordan1.us.oracle.com>
From:   Yang Shi <yang.shi@linux.alibaba.com>
Message-ID: <6cca9634-02c6-03fc-eeb2-9a4d54441ee1@linux.alibaba.com>
Date:   Thu, 2 Apr 2020 16:14:44 -0700
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On 4/2/20 4:04 PM, Daniel Jordan wrote:
> On Sat, Mar 28, 2020 at 03:29:40AM +0800, Yang Shi wrote:
>> Since the commit 8f182270dfec ("mm/swap.c: flush lru pvecs on compound
>> page arrival") THP would not stay in pagevec anymore.  So the
>> optimization made by commit d965432234db ("thp: increase
>> split_huge_page() success rate") doesn't make sense anymore, which tries
>> to unpin munlocked THPs from pagevec by draining pagevec.
>>
>> And draining lru cache before isolating THP in mlock path is unnecessary
>> either.
> Can we get some of that nice history in this part too?
>
> Draining lru cache before isolating THP in mlock path is also unnecessary.
> b676b293fb48 ("mm, thp: fix mapped pages avoiding unevictable list on mlock")
> added it and 9a73f61bdb8a ("thp, mlock: do not mlock PTE-mapped file huge
> pages") accidentally carried it over after the above optimization went in.

Thanks for finding out this, I didn't dig that far. Will add it into v2.

>
>> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
>> Cc: Hugh Dickins <hughd@google.com>
>> Cc: Andrea Arcangeli <aarcange@redhat.com>
>> Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>
> Since we don't mlock pte-mapped THP, it seems these huge pages wouldn't ever be
> in the pagevecs if I'm understanding it all.

Yes, it is correct.

>
> Saves lines and some amount of overhead and lru contention, so looks good.
>
> Reviewed-by: Daniel Jordan <daniel.m.jordan@oracle.com>

Thanks.