linux-kernel - Re: [PATCH -V2 4/5] swap: remove get/put_swap_device() in __swap

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Message-ID: <87o7mbyifo.fsf@yhuang6-desk2.ccr.corp.intel.com>
Date:   Tue, 23 May 2023 08:56:11 +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 4/5] swap: remove get/put_swap_device() in
 __swap_duplicate()

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

> On 22.05.23 09:09, Huang Ying wrote:
>> __swap_duplicate() is called by
>> - swap_shmem_alloc(): the page lock of the swap cache is held.
>
> page lock of the swap cache? Did you really mean to say that or am I
> confused?
>
> "Page lock of the page that is in the swap cache?"

Sorry for my poor English. Or make it shorter?

"the folio in the swap cache is locked"

Best Regards,
Huang, Ying

>> - copy_nonpresent_pte() -> swap_duplicate() and try_to_unmap_one()
>> ->
>>    swap_duplicate(): the page table lock is held.
>> - __read_swap_cache_async() -> swapcache_prepare(): enclosed with
>>    get/put_swap_device() in __read_swap_cache_async() already.
>> So, it's safe to remove get/put_swap_device() in __swap_duplicate().