Re: (resend)WARNING: trying to isolate tail page in isolate_lru_page

["Yin, Fengwei" <fengwei.yin@intel.com>]

On 8/26/2022 2:46 AM, Matthew Wilcox wrote:
>>> Looks like my analysis from yesterday was dropped:
>>>
>>> : This all seems quite plausible.  The reproducer seems to (correct me
>>> : if I'm wrong) create an AF_PACKET socket and mmap it.  af_packet.c
>>> : seems to create compound pages and mmap them.  This isn't folio-related
>>> : at all; I just moved the code that warns about it from mm/vmscan.c to
>>> : folio-compat.c.
>>> :
>>> : Looks like a long-standing bug in MADV_PAGEOUT to me.
>> Such page should never be on lru, right? We could test lru before
>> calling isolate_lru_page() for this case? I know isolate_lru_page()
>> does the check, but the tail page warning is raised before the check.
>>
>> Could the tail page warning be moved under the lru flag test? Seems
>> possible, but it should need extra handling (re-set lru flag). Seems a
>> little bit overkilling.
> There's a number of ways of solving this.  I'm interested in seeing
> which one Minchan thinks is best.
> 

My understanding is:
PageTransCompound() return false for compound page if THP is disabled
in kernel config. Replacing PageTransCompound() with PageCompound() 
could work here. But for the long term, folio should be the answer. :).


Regards
Yin, Fengwei