[PATCH 04/12] mm, thp, tmpfs: split huge page when moving from page cache to swap

[PATCH 04/12] mm, thp, tmpfs: split huge page when moving from page cache to swap

[Ning Qu]

in shmem_writepage, we have to split the huge page when moving pages
from page cache to swap because we don't support huge page in swap
yet.

Signed-off-by: Ning Qu <quning@gmail.com>
---
 mm/shmem.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/mm/shmem.c b/mm/shmem.c
index 8fe17dd..68a0e1d 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -898,6 +898,13 @@ static int shmem_writepage(struct page *page, struct writeback_control *wbc)
 	swp_entry_t swap;
 	pgoff_t index;
 
+	/* TODO: we have to break the huge page at this point,
+	 * since we have no idea how to recover a huge page from
+	 * swap.
+	 */
+	if (PageTransCompound(page))
+		split_huge_page(compound_trans_head(page));
+
 	BUG_ON(!PageLocked(page));
 	mapping = page->mapping;
 	index = page->index;
@@ -946,7 +953,7 @@ static int shmem_writepage(struct page *page, struct writeback_control *wbc)
 			if (shmem_falloc)
 				goto redirty;
 		}
-		clear_highpage(page);
+		clear_pagecache_page(page);
 		flush_dcache_page(page);
 		SetPageUptodate(page);
 	}
-- 
1.8.4

RE: [PATCH 04/12] mm, thp, tmpfs: split huge page when moving from page cache to swap

[Kirill A. Shutemov]

Ning Qu wrote:
> in shmem_writepage, we have to split the huge page when moving pages
> from page cache to swap because we don't support huge page in swap
> yet.
> 
> Signed-off-by: Ning Qu <quning@gmail.com>
> ---
>  mm/shmem.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/shmem.c b/mm/shmem.c
> index 8fe17dd..68a0e1d 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -898,6 +898,13 @@ static int shmem_writepage(struct page *page, struct writeback_control *wbc)
>  	swp_entry_t swap;
>  	pgoff_t index;
>  
> +	/* TODO: we have to break the huge page at this point,
> +	 * since we have no idea how to recover a huge page from
> +	 * swap.
> +	 */
> +	if (PageTransCompound(page))
> +		split_huge_page(compound_trans_head(page));
> +

After the split you handle here only first small page of the huge page.
Is it what we want to do? Should we swap out all small pages of the huge
page?

-- 
 Kirill A. Shutemov

Re: [PATCH 04/12] mm, thp, tmpfs: split huge page when moving from page cache to swap

[Ning Qu]

Let me take another look at that logic. Thanks!
Best wishes,
-- 
Ning Qu (曲宁) | Software Engineer | quning@google.com | +1-408-418-6066


On Tue, Oct 15, 2013 at 3:33 AM, Kirill A. Shutemov
<kirill.shutemov@linux.intel.com> wrote:
> Ning Qu wrote:
>> in shmem_writepage, we have to split the huge page when moving pages
>> from page cache to swap because we don't support huge page in swap
>> yet.
>>
>> Signed-off-by: Ning Qu <quning@gmail.com>
>> ---
>>  mm/shmem.c | 9 ++++++++-
>>  1 file changed, 8 insertions(+), 1 deletion(-)
>>
>> diff --git a/mm/shmem.c b/mm/shmem.c
>> index 8fe17dd..68a0e1d 100644
>> --- a/mm/shmem.c
>> +++ b/mm/shmem.c
>> @@ -898,6 +898,13 @@ static int shmem_writepage(struct page *page, struct writeback_control *wbc)
>>       swp_entry_t swap;
>>       pgoff_t index;
>>
>> +     /* TODO: we have to break the huge page at this point,
>> +      * since we have no idea how to recover a huge page from
>> +      * swap.
>> +      */
>> +     if (PageTransCompound(page))
>> +             split_huge_page(compound_trans_head(page));
>> +
>
> After the split you handle here only first small page of the huge page.
> Is it what we want to do? Should we swap out all small pages of the huge
> page?
>
> --
>  Kirill A. Shutemov