How to handle page allocation when memory exceeds a local node

[Won-Kyo Choe]

Suppose that there are two nodes and each node has 16GiB memory size.

When a process needs pages from the kernel, I understand that
__alloc_pages_nodemask() will do allocation for the process.

In the function, I noticed that if there is no available page on
a zone (or a node) while it loops for_next_zone_zonelist_nodemask()
(a macro in get_page_from_freelist()), the kernel would try to reclaim
reclaimable page from the zone. This loops will continue until the
kernel gets a free page. This means that the kernel would try to find a
page from the remote node if there is no free page in the local node.

My question is that when the kernel starts to allocate a page from the
remote node due to no enough memory in the local node, does the kernel
always check there is a reclaimable page from the local node?
In other words, does the kernel always start to find a page from the
very first entry (which would be the local node and the first zone)
in the loop?

In my perspective, if the kernel starts to allocate in the remote node,
I think the scheduler should move the process to the remote node and it
will allocate a page in the remote node at first in the loop (in the
process view, the node would be the local now since it is moved). Would
the scheduler do that?


Regards,
WK Choe