On 16.10.23 10:10, Yajun Deng wrote:
On 2023/10/16 14:33, Mike Rapoport wrote:
On Fri, Oct 13, 2023 at 05:29:19PM +0800, Yajun Deng wrote:
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,
after:
[ 0.260229] software IO TLB: area num 32.
[ 0.563497] Memory: 173413056K/199884452K available (18440K kernel code,
Memory:
Memory initialization is time consuming in the boot log.
You just confirmed that 56 msec is insignificant and then you send again
the improvement of ~60 msec in memory initialization.
What does this improvement gain in percentage of total boot time?
before:
[ 10.692708] Run /init as init process
after:
[ 10.666290] Run /init as init process
About 0.25%. The total boot time is variable, depending on how many
drivers need to be initialized.
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))
{'
No, it will not.
As the matter of fact any condition here won't be 'safer' because it makes
the code more complex and less maintainable.
Any future change in __free_pages_core() or one of it's callers will have
to reason what will happen with that condition after the change.
To avoid introducing MEMINIT_LATE context and make code simpler. This
might be a better option.
if (page_count(page) || PageReserved(page))
I'll have to side with Mike here; this change might not be worth it.
--
Cheers,
David / dhildenb
