Re: [RFC 2/3] mm: Add a new page flag PageLayzyFree() for MADV_FREE

[Huang\, Ying]

Wei Yang <richard.weiyang@xxxxxxxxx> writes:

> On Sun, Mar 15, 2020 at 10:54:03AM +0200, Mika Penttil?? wrote:
>>
>>
>>On 15.3.2020 10.18, Wei Yang wrote:
>>> On Fri, Feb 28, 2020 at 11:38:18AM +0800, Huang, Ying wrote:
>>> > From: Huang Ying <ying.huang@xxxxxxxxx>
>>> > 
>>> > Now !PageSwapBacked() is used as the flag for the pages freed lazily
>>> > via MADV_FREE.  This isn't obvious enough.  So Dave suggested to add a
>>> > new page flag for that to improve the code readability.
>>> I am confused with the usage of PageSwapBacked().
>>> 
>>> Previously I thought this flag means the page is swapin, set in
>>> swapin_readahead(). While I found page_add_new_anon_rmap() would set it too.
>>> This means every anon page would carry this flag. Then what is this flag
>>> means?
>>> 
>>> 
>>
>>But not all PageSwapBacked() pages are anon, like shmem.
>>
>
> Yes, while it looks shmem is the only exception.

Another exception is the pages freed lazily via MADV_FREE.

> I am still struggling to understand the meaning of this flag.

You can use `git blame` to find out the commit which introduces this
flag.  Which describes why this flag is introduced.

Best Regards,
Huang, Ying

>>
>>--Mika