RE: [PATCH 07/12] mm, thp, tmpfs: handle huge page in shmem_undo_range for truncate

["Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>]

Ning Qu wrote:
> When comes to truncate file, add support to handle huge page in the
> truncate range.
> 
> Signed-off-by: Ning Qu <quning@gmail.com>
> ---
>  mm/shmem.c | 97 +++++++++++++++++++++++++++++++++++++++++++++++++++++++-------
>  1 file changed, 86 insertions(+), 11 deletions(-)
> 
> diff --git a/mm/shmem.c b/mm/shmem.c
> index 0a423a9..90f2e0e 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -559,6 +559,7 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, loff_t lend,
>  	struct shmem_inode_info *info = SHMEM_I(inode);
>  	pgoff_t start = (lstart + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
>  	pgoff_t end = (lend + 1) >> PAGE_CACHE_SHIFT;
> +	/* Whether we have to do partial truncate */
>  	unsigned int partial_start = lstart & (PAGE_CACHE_SIZE - 1);
>  	unsigned int partial_end = (lend + 1) & (PAGE_CACHE_SIZE - 1);
>  	struct pagevec pvec;
> @@ -570,12 +571,16 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, loff_t lend,
>  	if (lend == -1)
>  		end = -1;	/* unsigned, so actually very big */
>  
> +	i_split_down_read(inode);
>  	pagevec_init(&pvec, 0);
>  	index = start;
>  	while (index < end) {
> +		bool thp = false;
> +
>  		pvec.nr = shmem_find_get_pages_and_swap(mapping, index,
>  				min(end - index, (pgoff_t)PAGEVEC_SIZE),
>  							pvec.pages, indices);
> +
>  		if (!pvec.nr)
>  			break;
>  		mem_cgroup_uncharge_start();
> @@ -586,6 +591,25 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, loff_t lend,
>  			if (index >= end)
>  				break;
>  
> +			thp = PageTransHugeCache(page);
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE_PAGECACHE

Again. Here and below ifdef is redundant: PageTransHugeCache() is zero
compile-time and  thp case will be optimize out.

And do we really need a copy of truncate logic here? Is there a way to
share code?

-- 
 Kirill A. Shutemov

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