linux-kernel - Re: [PATCH v3] memory_hotplug: Free pages as higher order

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Date:   Thu, 27 Sep 2018 13:41:45 +0530
From:   Arun KS <arunks@...eaurora.org>
To:     Juergen Gross <jgross@...e.com>
Cc:     kys@...rosoft.com, haiyangz@...rosoft.com, sthemmin@...rosoft.com,
        boris.ostrovsky@...cle.com, akpm@...ux-foundation.org,
        dan.j.williams@...el.com, mhocko@...e.com, vbabka@...e.cz,
        iamjoonsoo.kim@....com, gregkh@...uxfoundation.org,
        osalvador@...e.de, malat@...ian.org,
        kirill.shutemov@...ux.intel.com, jrdr.linux@...il.com,
        yasu.isimatu@...il.com, mgorman@...hsingularity.net,
        aaron.lu@...el.com, devel@...uxdriverproject.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        xen-devel@...ts.xenproject.org, vatsa@...eaurora.org,
        vinmenon@...eaurora.org, getarunks@...il.com
Subject: Re: [PATCH v3] memory_hotplug: Free pages as higher order

On 2018-09-27 12:41, Juergen Gross wrote:
> On 27/09/18 08:58, Arun KS wrote:
>> When free pages are done with higher order, time spend on
>> coalescing pages by buddy allocator can be reduced. With
>> section size of 256MB, hot add latency of a single section
>> shows improvement from 50-60 ms to less than 1 ms, hence
>> improving the hot add latency by 60%.
>> 
>> Modify external providers of online callback to align with
>> the change.
>> 
>> Signed-off-by: Arun KS <arunks@...eaurora.org>
>> ---
>> Changes since v2:
>> reuse code from __free_pages_boot_core()
>> 
>> Changes since v1:
>> - Removed prefetch()
>> 
>> Changes since RFC:
>> - Rebase.
>> - As suggested by Michal Hocko remove pages_per_block.
>> - Modifed external providers of online_page_callback.
>> 
>> v2: https://lore.kernel.org/patchwork/patch/991363/
>> v1: https://lore.kernel.org/patchwork/patch/989445/
>> RFC: https://lore.kernel.org/patchwork/patch/984754/
>> 
>> ---
>>  drivers/hv/hv_balloon.c        |  6 ++++--
>>  drivers/xen/balloon.c          | 18 ++++++++++++++---
>>  include/linux/memory_hotplug.h |  2 +-
>>  mm/internal.h                  |  1 +
>>  mm/memory_hotplug.c            | 44 
>> ++++++++++++++++++++++++++++++------------
>>  mm/page_alloc.c                |  2 +-
>>  6 files changed, 54 insertions(+), 19 deletions(-)
>> 
> 
> ...
> 
>> diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
>> index e12bb25..010cf4d 100644
>> --- a/drivers/xen/balloon.c
>> +++ b/drivers/xen/balloon.c
>> @@ -390,8 +390,8 @@ static enum bp_state 
>> reserve_additional_memory(void)
>> 
>>  	/*
>>  	 * add_memory_resource() will call online_pages() which in its turn
>> -	 * will call xen_online_page() callback causing deadlock if we don't
>> -	 * release balloon_mutex here. Unlocking here is safe because the
>> +	 * will call xen_bring_pgs_online() callback causing deadlock if we
>> +	 * don't release balloon_mutex here. Unlocking here is safe because 
>> the
>>  	 * callers drop the mutex before trying again.
>>  	 */
>>  	mutex_unlock(&balloon_mutex);
>> @@ -422,6 +422,18 @@ static void xen_online_page(struct page *page)
>>  	mutex_unlock(&balloon_mutex);
>>  }
>> 
>> +static int xen_bring_pgs_online(struct page *pg, unsigned int order)
>> +{
>> +	unsigned long i, size = (1 << order);
>> +	unsigned long start_pfn = page_to_pfn(pg);
>> +
>> +	pr_debug("Online %lu pages starting at pfn 0x%lx\n", size, 
>> start_pfn);
>> +	for (i = 0; i < size; i++)
>> +		xen_online_page(pfn_to_page(start_pfn + i));
> 

Hi,

> xen_online_page() isn't very complex and this is the only user.
> 
> Why don't you move its body in here and drop the extra function?
> And now you can execute the loop with balloon_mutex held instead of
> taking and releasing it in each iteration of the loop.
Point taken. Will incorporate them.

Regards,
Arun
> 
> 
> Juergen