Re: [PATCH] mm,thp,shmem: limit shmem THP alloc gfp_mask

[Vlastimil Babka <vbabka@suse.cz>]

On 10/22/20 4:51 PM, Vlastimil Babka wrote:
> On 10/22/20 5:48 AM, Rik van Riel wrote:
>> The allocation flags of anonymous transparent huge pages can be controlled
>> through the files in /sys/kernel/mm/transparent_hugepage/defrag, which can
>> help the system from getting bogged down in the page reclaim and compaction
>> code when many THPs are getting allocated simultaneously.
>> 
>> However, the gfp_mask for shmem THP allocations were not limited by those
>> configuration settings, and some workloads ended up with all CPUs stuck
>> on the LRU lock in the page reclaim code, trying to allocate dozens of
>> THPs simultaneously.
>> 
>> This patch applies the same configurated limitation of THPs to shmem
>> hugepage allocations, to prevent that from happening.
>> 
>> This way a THP defrag setting of "never" or "defer+madvise" will result
>> in quick allocation failures without direct reclaim when no 2MB free
>> pages are available.
>> 
>> Signed-off-by: Rik van Riel <riel@surriel.com>
> 
> FTR, a patch to the same effect was sent by Xu Yu:

Hm thought I did CC, but TB ate it. sorry for the noise

> https://lore.kernel.org/r/11e1ead211eb7d141efa0eb75a46ee2096ee63f8.1603267572.git.xuyu@linux.alibaba.com
> 
>> ---
>> 
>> diff --git a/include/linux/gfp.h b/include/linux/gfp.h
>> index c603237e006c..0a5b164a26d9 100644
>> --- a/include/linux/gfp.h
>> +++ b/include/linux/gfp.h
>> @@ -614,6 +614,8 @@ bool gfp_pfmemalloc_allowed(gfp_t gfp_mask);
>>   extern void pm_restrict_gfp_mask(void);
>>   extern void pm_restore_gfp_mask(void);
>>   
>> +extern gfp_t alloc_hugepage_direct_gfpmask(struct vm_area_struct *vma);
>> +
>>   #ifdef CONFIG_PM_SLEEP
>>   extern bool pm_suspended_storage(void);
>>   #else
>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>> index 9474dbc150ed..9b08ce5cc387 100644
>> --- a/mm/huge_memory.c
>> +++ b/mm/huge_memory.c
>> @@ -649,7 +649,7 @@ static vm_fault_t __do_huge_pmd_anonymous_page(struct vm_fault *vmf,
>>    *	    available
>>    * never: never stall for any thp allocation
>>    */
>> -static inline gfp_t alloc_hugepage_direct_gfpmask(struct vm_area_struct *vma)
>> +gfp_t alloc_hugepage_direct_gfpmask(struct vm_area_struct *vma)
>>   {
>>   	const bool vma_madvised = !!(vma->vm_flags & VM_HUGEPAGE);
>>   
>> diff --git a/mm/shmem.c b/mm/shmem.c
>> index 537c137698f8..d1290eb508e5 100644
>> --- a/mm/shmem.c
>> +++ b/mm/shmem.c
>> @@ -1545,8 +1545,11 @@ static struct page *shmem_alloc_hugepage(gfp_t gfp,
>>   		return NULL;
>>   
>>   	shmem_pseudo_vma_init(&pvma, info, hindex);
>> -	page = alloc_pages_vma(gfp | __GFP_COMP | __GFP_NORETRY | __GFP_NOWARN,
>> -			HPAGE_PMD_ORDER, &pvma, 0, numa_node_id(), true);
>> +	/* Limit the gfp mask according to THP configuration. */
>> +	gfp |= __GFP_COMP | __GFP_NORETRY | __GFP_NOWARN;
>> +	gfp &= alloc_hugepage_direct_gfpmask(&pvma);
>> +	page = alloc_pages_vma(gfp, HPAGE_PMD_ORDER, &pvma, 0, numa_node_id(),
>> +			       true);
>>   	shmem_pseudo_vma_destroy(&pvma);
>>   	if (page)
>>   		prep_transhuge_page(page);
>> 
>