linux-kernel - Re: [PATCH] mm: shmem: implement POSIX_FADV

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Date:   Wed, 3 Nov 2021 18:11:00 +0530
From:   Charan Teja Kalla <charante@...eaurora.org>
To:     Suren Baghdasaryan <surenb@...gle.com>
Cc:     hughd@...gle.com, akpm@...ux-foundation.org, vbabka@...e.cz,
        rientjes@...gle.com, david@...hat.com, mhocko@...e.com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        kirill.shutemov@...ux.intel.com, rppt@...ux.vnet.ibm.com,
        guptap@...eaurora.org
Subject: Re: [PATCH] mm: shmem: implement POSIX_FADV_[WILL|DONT]NEED for shmem

Thanks Suren for the reply!!

On 11/2/2021 11:42 PM, Suren Baghdasaryan wrote:
>>> Also not sure if you need to isolate the page before this writeback.
>> Isolation may not be required but this is to avoid trying of the reclaim
>> on the same page in some parallel path as both any way places the page
>> in the swap. Or you want me to remove the isolation here?
> Maybe you could isolate them in bulk then? Seems like a waste
> isolating them one-by-one.

Okay. Should the bulk here be SWAP_CLUSTER_MAX fine?

> 
>>> Won't deleting the page from swap cache interfere with ongoing
>>> writeback if it has not yet completed?
>> I just followed the path of how to reclaim the page:
>> shrink_page_list()
>>      pageout()
>>      ..........
>>      __remove_mapping()
>>         __delete_from_swap_cache()
>>
>> You see some issue here which I can't understand.
> I think shrink_page_list() would not call __remove_mapping() if after
> pageout() PageWriteback() is still true. Maybe I'm missing some path?

I agree here. PG_writeback might have still set on the pages under
background writeback thus should be excluded.

I just considered the case for sync writes, eg:zram,  where PG_writeback
is cleared before returns.

Will update the change accordingly.

> 

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