Re: [RFC 0/3] mm: Discard lazily freed pages when migrating

Matthew Wilcox
2020-02-28T03:42:54Z

On Fri, Feb 28, 2020 at 11:38:16AM +0800, Huang, Ying wrote:
> MADV_FREE is a lazy free mechanism in Linux. According to the manpage
> of mavise(2), the semantics of MADV_FREE is,
>
> The application no longer requires the pages in the range specified
> by addr and len. The kernel can thus free these pages, but the
> freeing could be delayed until memory pressure occurs. ...
>
> Originally, the pages freed lazily by MADV_FREE will only be freed
> really by page reclaiming when there is memory pressure or when
> unmapping the address range. In addition to that, there's another
> opportunity to free these pages really, when we try to migrate them.
>
> The main value to do that is to avoid to create the new memory
> pressure immediately if possible. Instead, even if the pages are
> required again, they will be allocated gradually on demand. That is,
> the memory will be allocated lazily when necessary. This follows the
> common philosophy in the Linux kernel, allocate resources lazily on
> demand.

Do you have an example program which does this (and so benefits)?
If so, can you quantify the benefit at all?