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Subject: Re: [PATCH] mm: make munlock fast when mlock is canceled by sigkill
From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Minchan Kim <minchan.kim@gmail.com>,
       Hiroaki Wakabayashi <primulaelatior@gmail.com>,
       Andrew Morton <akpm@linux-foundation.org>,
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       Paul Menage <menage@google.com>, Ying Han <yinghan@google.com>,
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       Lee Schermerhorn <lee.schermerhorn@hp.com>
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> This patch is for making commit 4779280d1e (mm: make get_user_pages()
> interruptible) complete.

Yes.
commit 4779280d1e (mm: make get_user_pages() interruptible) has never
works as expected since it's born.
IOW, it was totally broken.

This patch is definitely good forward step patch.


>> > @@ -254,6 +254,7 @@ static inline void
>> > mminit_validate_memmodel_limits(unsigned long *start_pfn,
>> >  #define GUP_FLAGS_FORCE                  0x2
>> >  #define GUP_FLAGS_IGNORE_VMA_PERMISSIONS 0x4
>> >  #define GUP_FLAGS_IGNORE_SIGKILL         0x8
>> > +#define GUP_FLAGS_ALLOW_NULL             0x10
>> >
>>
>> I am worried about adding new flag whenever we need it.
>> But I think this case makes sense to me.
>> In addition, I guess ZERO page can also use this flag.
>>
>> Kame. What do you think about it?
>>
> I do welcome this !
> Then, I don't have to take care of mlock/munlock in ZERO_PAGE patch.
>
> And without this patch, munlock() does copy-on-write just for unpinning memory.
> So, this patch shows some right direction, I think.
>
> One concern is flag name, ALLOW_NULL sounds not very good.
>
>  GUP_FLAGS_NOFAULT ?
>
> I wonder we can remove a hack of FOLL_ANON for core-dump by this flag, too.

Yeah, GUP_FLAGS_NOFAULT is better.

Plus, this patch change __get_user_pages() return value meaning IOW.
after this patch, it can return following value,

 return value: 3
 pages[0]: hoge-page
 pages[1]: null
 pages[2]: fuga-page

but, it can be

 return value: 2
 pages[0]: hoge-page
 pages[1]: fuga-page

no?