Hi Mel,
在 2024/9/4 19:13, Mel Gorman 写道:
On Mon, Sep 02, 2024 at 08:24:43PM +0800, Rong Qianfeng wrote:
Reserved pages are basically non-lru pages. This kind of memory can't be
used as migration sources and targets, skip it can bring some performance
benefits.
Because some drivers may also use PG_reserved, we just set PB_migrate_skip
for those clustered reserved bootmem during memory initialization.
Signed-off-by: Rong Qianfeng <rongqianfeng@xxxxxxxx>
I'm not convinced the savings due to skipping a few pages during the scan
would justify the additional code. There would have to be a large number
of reserved pages scattered throughout the zone to make a difference and
even that situation would be a big surprise. I'm not even sure this can be
explicitly tested unless you artifically create reserved pages throughout the
zone, which would not be convincing, or know if a driver that exhibits such
behaviour in which case my first question is -- what is that driver doing?!?
Thanks for taking the time to reply.
At first I thought that there was not much PageReserved pages, but when I
looked at the memory initialization code, I found that no-map pages were
also marked as PageReserved. On mobile platforms, there is a lot of no-map
pages (for example, ARM64 MT6991 no-map pages has 1065MB). These
pages are usually used by various hardware subsystems such as modem. So
I think it makes sense to skip these pages.
//no-map and reserved memory marked as PageReserved
static void __init memmap_init_reserved_pages(void)
{
...
for_each_mem_region(region) {
...
if (memblock_is_nomap(region))
reserve_bootmem_region(start, end, nid); //for no-map memory
memblock_set_node(start, end, &memblock.reserved, nid);
}
for_each_reserved_mem_region(region) {
if (!memblock_is_reserved_noinit(region)) {
...
reserve_bootmem_region(start, end, nid); //for reserved memory
}
}
}
Best Regards,
Qianfeng
