On 18 Feb 2019, at 9:42, Vlastimil Babka wrote:
On 2/18/19 6:31 PM, Zi Yan wrote:
The purpose of proposing exchange_pages() is to avoid allocating any
new
page,
so that we would not trigger any potential page reclaim or memory
compaction.
Allocating a temporary page defeats the purpose.
Compaction can only happen for order > 0 temporary pages. Even if you
used
single order = 0 page to gradually exchange e.g. a THP, it should be
better than
u64. Allocating order = 0 should be a non-issue. If it's an issue,
then the
system is in a bad state and physically contiguous layout is a
secondary concern.
You are right if we only need to allocate one order-0 page. But this
also means
we can only exchange two pages at a time. We need to add a lock to make
sure
the temporary page is used exclusively or we need to keep allocating
temporary pages
when multiple exchange_pages() are happening at the same time.
--
Best Regards,
Yan Zi
