On 2023/10/13 16:48, Mike Rapoport wrote:
On Thu, Oct 12, 2023 at 05:53:22PM +0800, Yajun Deng wrote:
On 2023/10/12 17:23, David Hildenbrand wrote:
On 10.10.23 04:31, Yajun Deng wrote:
On 2023/10/8 16:57, Yajun Deng wrote:
That looks wrong. if the page count would by pure luck be 0
already for hotplugged memory, you wouldn't clear the reserved
flag.
These changes make me a bit nervous.
Is 'if (page_count(page) || PageReserved(page))' be safer? Or do I
need to do something else?
How about the following if statement? But it needs to add more patch
like v1 ([PATCH 2/4] mm: Introduce MEMINIT_LATE context).
It'll be safer, but more complex. Please comment...
if (context != MEMINIT_EARLY || (page_count(page) ||
PageReserved(page)) {
Ideally we could make initialization only depend on the context, and not
check for count or the reserved flag.
This link is v1,
https://lore.kernel.org/all/20230922070923.355656-1-yajun.deng@xxxxxxxxx/
If we could make initialization only depend on the context, I'll modify it
based on v1.
Although ~20% improvement looks impressive, this is only optimization of a
fraction of the boot time, and realistically, how much 56 msec saves from
the total boot time when you boot a machine with 190G of RAM?
There are a lot of factors that can affect the total boot time. 56 msec
saves may be insignificant.
But if we look at the boot log, we'll see there's a significant time jump.
before:
[ 0.250334] ACPI: PM-Timer IO Port: 0x508
[ 0.618994] Memory: 173413056K/199884452K available (18440K kernel
code, 4204K rwdata, 5608K rodata, 3188K init, 17024K bss, 5499616K
reserved, 20971520K cma-reserved)
after:
[ 0.260229] software IO TLB: area num 32.
[ 0.563497] Memory: 173413056K/199884452K available (18440K kernel
code, 4204K rwdata, 5608K rodata, 3188K init, 17024K bss, 5499616K
reserved, 20971520K cma-reserved)
Memory initialization is time consuming in the boot log.
I still think the improvement does not justify the churn, added complexity
and special casing of different code paths of initialization of struct pages.
Because there is a loop, if the order is MAX_ORDER, the loop will run
1024 times. The following 'if' would be safer:
'if (context != MEMINIT_EARLY || (page_count(page) || >>
PageReserved(page)) {'
This is a foundation. We may change this when we are able to safely
remove page init in the hotplug context one day.
So the case for the early context is only temporary.
@Mike, By the way, this code will cost more time:
if (context == MEMINIT_HOTPLUG)
flags = INIT_PAGE_COUNT | INIT_PAGE_RESERVED;
__init_single_page(page, pfn, zone, nid, flags);
[ 0.014999] On node 0, zone DMA32: 31679 pages in unavailable ranges
[ 0.311560] ACPI: PM-Timer IO Port: 0x508
This code will cost less time:
__init_single_page(page, pfn, zone, nid, 0);
if (context == MEMINIT_HOTPLUG) {
init_page_count(page);
__SetPageReserved(page);
[ 0.014299] On node 0, zone DMA32: 31679 pages in unavailable ranges
[ 0.250223] ACPI: PM-Timer IO Port: 0x508
