Re: [PATCH 0/6] migration/postcopy: enable compress during postcopy

[Wei Yang <richardw.yang@linux.intel.com>]

On Thu, Nov 07, 2019 at 09:15:44AM +0000, Dr. David Alan Gilbert wrote:
>* Wei Yang (richardw.yang@linux.intel.com) wrote:
>> On Wed, Nov 06, 2019 at 08:11:44PM +0000, Dr. David Alan Gilbert wrote:
>> >* Wei Yang (richardw.yang@linux.intel.com) wrote:
>> >> This patch set tries enable compress during postcopy.
>> >> 
>> >> postcopy requires to place a whole host page, while migration thread migrate
>> >> memory in target page size. This makes postcopy need to collect all target
>> >> pages in one host page before placing via userfaultfd.
>> >> 
>> >> To enable compress during postcopy, there are two problems to solve:
>> >> 
>> >>     1. Random order for target page arrival
>> >>     2. Target pages in one host page arrives without interrupt by target
>> >>        page from other host page
>> >> 
>> >> The first one is handled by counting the number of target pages arrived
>> >> instead of the last target page arrived.
>> >> 
>> >> The second one is handled by:
>> >> 
>> >>     1. Flush compress thread for each host page
>> >>     2. Wait for decompress thread for before placing host page
>> >> 
>> >> With the combination of these two changes, compress is enabled during
>> >> postcopy.
>> >
>> >What have you tested this with? 2MB huge pages I guess?
>> >
>> 
>> I tried with this qemu option:
>> 
>>    -object memory-backend-file,id=mem1,mem-path=/dev/hugepages/guest2,size=4G \
>>    -device pc-dimm,id=dimm1,memdev=mem1
>> 
>> /dev/hugepages/guest2 is a file under hugetlbfs
>> 
>>    hugetlbfs on /dev/hugepages type hugetlbfs (rw,relatime,pagesize=2M)
>
>OK, yes that should be fine.
>I suspect on Power/ARM where they have normal memory with 16/64k pages,
>the cost of the flush will mean compression is more expensive in
>postcopy mode; but still makes it possible.
>

Not get your point clearly about more expensive. You mean more expensive on
ARM/Power?

If the solution looks good to you, I would prepare v2.

>Dave
>
>> >Dave
>> >
>> >> Wei Yang (6):
>> >>   migration/postcopy: reduce memset when it is zero page and
>> >>     matches_target_page_size
>> >>   migration/postcopy: wait for decompress thread in precopy
>> >>   migration/postcopy: count target page number to decide the
>> >>     place_needed
>> >>   migration/postcopy: set all_zero to true on the first target page
>> >>   migration/postcopy: enable random order target page arrival
>> >>   migration/postcopy: enable compress during postcopy
>> >> 
>> >>  migration/migration.c | 11 --------
>> >>  migration/ram.c       | 65 ++++++++++++++++++++++++++++++-------------
>> >>  2 files changed, 45 insertions(+), 31 deletions(-)
>> >> 
>> >> -- 
>> >> 2.17.1
>> >> 
>> >--
>> >Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
>> 
>> -- 
>> Wei Yang
>> Help you, Help me
>--
>Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK

-- 
Wei Yang
Help you, Help me