Re: [PATCH 1/1] mm/khugepaged: skip copying lazyfree pages on collapse

[Michal Hocko]

On Thu 01-02-24 20:52:26, Lance Yang wrote:
> The collapsing behavior of khugepaged with pages
> marked using MADV_FREE might cause confusion
> among users.
> 
> For instance, allocate a 2MB chunk using mmap and
> later release it by MADV_FREE. Khugepaged will not
> collapse this chunk. From the user's perspective,
> it treats lazyfree pages as pte_none. However,
> for some pages marked as lazyfree with MADV_FREE,
> khugepaged might collapse this chunk and copy
> these pages to a new huge page. This inconsistency
> in behavior could be confusing for users.

Is that any more confusing than collapsing pte_none
pages?

TBH I do not really see why this is a problem. MADV_FREE
are correctly recognized same as pte_none so the user
defined trashold applies.
-- 
Michal Hocko
SUSE Labs