linux-kernel - Re: [PATCH v6 4/6] khugepaged: rename collapse_shmem() and khugepaged_scan

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Date:   Sat, 22 Jun 2019 04:48:25 +0000
From:   Song Liu <songliubraving@...com>
To:     Hillf Danton <hdanton@...a.com>
CC:     Linux-MM <linux-mm@...ck.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        Kernel Team <Kernel-team@...com>,
        "william.kucharski@...cle.com" <william.kucharski@...cle.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
Subject: Re: [PATCH v6 4/6] khugepaged: rename collapse_shmem() and
 khugepaged_scan_shmem()



> On Jun 21, 2019, at 8:11 PM, Hillf Danton <hdanton@...a.com> wrote:
> 
> 
> Hello
> 
> On Fri, 21 Jun 2019 17:05:10 -0700 Song Liu <songliubraving@...com> wrote:
>> Next patch will add khugepaged support of non-shmem files. This patch
>> renames these two functions to reflect the new functionality:
>> 
>>    collapse_shmem()        =>  collapse_file()
>>    khugepaged_scan_shmem() =>  khugepaged_scan_file()
>> 
>> Acked-by: Rik van Riel <riel@...riel.com>
>> Signed-off-by: Song Liu <songliubraving@...com>
>> ---
>> mm/khugepaged.c | 13 +++++++------
>> 1 file changed, 7 insertions(+), 6 deletions(-)
>> 
>> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
>> index 0f7419938008..dde8e45552b3 100644
>> --- a/mm/khugepaged.c
>> +++ b/mm/khugepaged.c
>> @@ -1287,7 +1287,7 @@ static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff)
>> }
>> 
>> /**
>> - * collapse_shmem - collapse small tmpfs/shmem pages into huge one.
>> + * collapse_file - collapse small tmpfs/shmem pages into huge one.
>>  *
>>  * Basic scheme is simple, details are more complex:
>>  *  - allocate and lock a new huge page;
>> @@ -1304,10 +1304,11 @@ static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff)
>>  *    + restore gaps in the page cache;
>>  *    + unlock and free huge page;
>>  */
>> -static void collapse_shmem(struct mm_struct *mm,
>> +static void collapse_file(struct vm_area_struct *vma,
>> 		struct address_space *mapping, pgoff_t start,
>> 		struct page **hpage, int node)
>> {
>> +	struct mm_struct *mm = vma->vm_mm;
>> 	gfp_t gfp;
>> 	struct page *new_page;
>> 	struct mem_cgroup *memcg;
>> @@ -1563,7 +1564,7 @@ static void collapse_shmem(struct mm_struct *mm,
>> 	/* TODO: tracepoints */
>> }
>> 
>> -static void khugepaged_scan_shmem(struct mm_struct *mm,
>> +static void khugepaged_scan_file(struct vm_area_struct *vma,
>> 		struct address_space *mapping,
>> 		pgoff_t start, struct page **hpage)
>> {
>> @@ -1631,14 +1632,14 @@ static void khugepaged_scan_shmem(struct mm_struct *mm,
>> 			result = SCAN_EXCEED_NONE_PTE;
>> 		} else {
>> 			node = khugepaged_find_target_node();
>> -			collapse_shmem(mm, mapping, start, hpage, node);
>> +			collapse_file(vma, mapping, start, hpage, node);
>> 		}
>> 	}
>> 
>> 	/* TODO: tracepoints */
>> }
>> #else
>> -static void khugepaged_scan_shmem(struct mm_struct *mm,
>> +static void khugepaged_scan_file(struct vm_area_struct *vma,
>> 		struct address_space *mapping,
>> 		pgoff_t start, struct page **hpage)
>> {
>> @@ -1722,7 +1723,7 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages,
>> 				file = get_file(vma->vm_file);
>> 				up_read(&mm->mmap_sem);
>> 				ret = 1;
>> -				khugepaged_scan_shmem(mm, file->f_mapping,
>> +				khugepaged_scan_file(vma, file->f_mapping,
>> 						pgoff, hpage);
>> 				fput(file);
> 
> Is it a change that should have put some material in the log message?
> Is it unlikely for vma to go without mmap_sem held?

This is a great point. We really need to be more careful. Let me fix 
it in the next version. 

Thanks,
Song