[CRIU] [PATCH 2/3] mem: if no parent image persists, can't rely on it

[Pavel Tikhomirov]

Please read this comment.


Best Regards, Tikhomirov Pavel.


2014-04-15 17:43 GMT+04:00 Pavel Tikhomirov <snorcht at gmail.com>:

> Ok, but what if parent writes to memory first and gets COW'ed,
> and child gets writable memory when access it.
> It can result in no PF.
>
> Just an Idea, need to understand COW mechanism more precisely.
>
>
> Best Regards, Tikhomirov Pavel.
>
>
> 2014-04-15 17:03 GMT+04:00 Cyrill Gorcunov <gorcunov at gmail.com>:
>
> On Tue, Apr 15, 2014 at 04:48:33PM +0400, Pavel Tikhomirov wrote:
>> >    It seem to me, that clear_soft_dirty function for pte in kernel is
>> called
>> >    only
>> >    if we had explicit write to /proc/pid/clear_refs. Only after that all
>> >    pages will
>> >    become write-protected and dirty tracking realy works, if new
>> process was
>> >    created between snapshots, some part of its memory can be not write
>> >    protected so no PF generated for this part and some soft-dirty bits
>> not
>> >    set,
>> >    isn't it?
>>
>> No, when new process created and executed -- new memory will all be marked
>> as soft-dirty. If new process is created with fork() then its pages will
>> be COW'ed and once write fault happened the page will be marked as soft
>> dirty as far as I remember.
>>
>
>
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