Re: [RFCv2 3/6] mm: introduce MADV_PAGEOUT

On Fri, May 31, 2019 at 10:50:44AM +0200, Michal Hocko wrote:

On Fri 31-05-19 15:43:10, Minchan Kim wrote:

quoted

When a process expects no accesses to a certain memory range
for a long time, it could hint kernel that the pages can be
reclaimed instantly but data should be preserved for future use.
This could reduce workingset eviction so it ends up increasing
performance.

This patch introduces the new MADV_PAGEOUT hint to madvise(2)
syscall. MADV_PAGEOUT can be used by a process to mark a memory
range as not expected to be used for a long time so that kernel
reclaims the memory instantly. The hint can help kernel in deciding
which pages to evict proactively.

Again, are there any restictions on what kind of memory can be paged out?
Private/Shared, anonymous/file backed. Any restrictions on mapping type.
Etc. Please make sure all that is in the changelog.

It's same with MADV_COLD. Yes, I will include all detail in the
description.

What are the failure modes? E.g. what if the swap is full, does the call
fails or it silently ignores the error?

In such case, just ignore the swapout. It returns -EINVAL only if the
vma is one of (VM_LOCKED|VM_HUGETLB|VM_PFNMAP) at this moment.

Thanks!
-- 
Michal Hocko
SUSE Labs