linux-kernel - Re: [PATCH][v3] mm/hugetlb: Retry to allocate for early boot hugepage allocation

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Message-ID: <bcf7e932-0a14-4cd9-b994-50114013d96b@redhat.com>
Date: Fri, 29 Aug 2025 21:20:14 +0200
From: David Hildenbrand <david@...hat.com>
To: "Li,Rongqing" <lirongqing@...du.com>,
 "muchun.song@...ux.dev" <muchun.song@...ux.dev>,
 "osalvador@...e.de" <osalvador@...e.de>,
 "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
 "linux-mm@...ck.org" <linux-mm@...ck.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "giorgitchankvetadze1997@...il.com" <giorgitchankvetadze1997@...il.com>
Subject: Re: [PATCH][v3] mm/hugetlb: Retry to allocate for early boot hugepage
 allocation

On 29.08.25 17:20, Li,Rongqing wrote:
> 
> 
>> On 29.08.25 11:52, lirongqing wrote:
>>> From: Li RongQing <lirongqing@...du.com>
>>>
>>> In cloud environments with massive hugepage reservations (95%+ of
>>> system RAM), single-attempt allocation during early boot often fails
>>> due to memory pressure.
>>>
>>> Commit 91f386bf0772 ("hugetlb: batch freeing of vmemmap pages")
>>> intensified this by deferring page frees, increase peak memory usage during
>> allocation.
>>>
>>> Introduce a retry mechanism that leverages vmemmap optimization
>>> reclaim (~1.6% memory) when available. Upon initial allocation
>>> failure, the system retries until successful or no further progress is
>>> made, ensuring reliable hugepage allocation while preserving batched
>> vmemmap freeing benefits.
>>>
>>> Testing on a 256G machine allocating 252G of hugepages:
>>> Before: 128056/129024 hugepages allocated
>>> After:  Successfully allocated all 129024 hugepages
>>>
>>> Suggested-by: David Hildenbrand <david@...hat.com>
>>> Signed-off-by: Li RongQing <lirongqing@...du.com>
>>> ---
>>> Diff with v2: auto retry mechanism
>>> Diff with v1: add log if two-phase hugepage allocation is triggered
>>> 		add the knod to control split ratio
>>>
>>>    mm/hugetlb.c | 27 +++++++++++++++++++++++----
>>>    1 file changed, 23 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 753f99b..18e54ea 100644
>>> --- a/mm/hugetlb.c
>>> +++ b/mm/hugetlb.c
>>> @@ -3589,10 +3589,9 @@ static unsigned long __init
>>> hugetlb_pages_alloc_boot(struct hstate *h)
>>>
>>>    	unsigned long jiffies_start;
>>>    	unsigned long jiffies_end;
>>> +	unsigned long remaining;
>>>
>>>    	job.thread_fn	= hugetlb_pages_alloc_boot_node;
>>> -	job.start	= 0;
>>> -	job.size	= h->max_huge_pages;
>>>
>>>    	/*
>>>    	 * job.max_threads is 25% of the available cpu threads by default.
>>> @@ -3616,10 +3615,30 @@ static unsigned long __init
>> hugetlb_pages_alloc_boot(struct hstate *h)
>>>    	}
>>>
>>>    	job.max_threads	= hugepage_allocation_threads;
>>> -	job.min_chunk	= h->max_huge_pages /
>> hugepage_allocation_threads;
>>>
>>>    	jiffies_start = jiffies;
>>> -	padata_do_multithreaded(&job);
>>> +	do {
>>> +		remaining = h->max_huge_pages - h->nr_huge_pages;
>>> +
>>> +		job.start     = h->nr_huge_pages;
>>> +		job.size      = remaining;
>>> +		job.min_chunk = remaining / hugepage_allocation_threads;
>>> +		padata_do_multithreaded(&job);
>>> +
>>> +		if (h->nr_huge_pages == h->max_huge_pages)
>>> +			break;
> 
> If all pages are allocated, it will break out from here. Since in most cases the first allocation is successful, I have moved this check to the very beginning.

Missed that, thanks!

> 
>>> +
>>> +		/*
>>> +		 * Retry allocation if vmemmap optimization is available, the
>>> +		 * optimization frees ~1.6% of memory of hugepages, this reclaimed
>>> +		 * memory enables additional hugepage allocations
>>
>> As I said, please remove any calculation details about the vmemmap.
>> That's not the place to have such calculations easily become stale.
>>
>> Something like the following:
>>
>> /*
>>    * Retry only if the vmemmap optimization might have been able to free
>>    * some memory back to the system.
>>    */
>>
> 
> Thanks, I will fix it
> 
>>> +		 */
>>> +		if (!hugetlb_vmemmap_optimizable(h))
>>> +			break;
>>> +
>>> +	/* Continue if progress was made in last iteration */
>>
>> Comment wrongly indented.
>>

Maybe just comment above the loop that we retry as long as we are making 
progress instead. It's unusual to see these tail comments in loops.

-- 
Cheers

David / dhildenb