Re: [PATCH v3.1 -mmotm 2/2] memcg: move charge of file pages

[Andrew Morton <akpm@linux-foundation.org>]

On Thu, 8 Apr 2010 17:08:58 +0900
Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote:

>
> ...
>
> This patch adds support for moving charge of file pages, which include normal
> file, tmpfs file and swaps of tmpfs file. It's enabled by setting bit 1 of
> <target cgroup>/memory.move_charge_at_immigrate. Unlike the case of anonymous
> pages, file pages(and swaps) in the range mmapped by the task will be moved even
> if the task hasn't done page fault, i.e. they might not be the task's "RSS",
> but other task's "RSS" that maps the same file. And mapcount of the page is
> ignored(the page can be moved even if page_mapcount(page) > 1). So, conditions
> that the page/swap should be met to be moved is that it must be in the range
> mmapped by the target task and it must be charged to the old cgroup.
> 
> Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
>
> ...
>
> +static struct page *mc_handle_file_pte(struct vm_area_struct *vma,
> +			unsigned long addr, pte_t ptent, swp_entry_t *entry)
> +{
> +	struct page *page = NULL;
> +	struct inode *inode;
> +	struct address_space *mapping;
> +	pgoff_t pgoff;
> +
> +	if (!vma->vm_file) /* anonymous vma */
> +		return NULL;
> +	if (!move_file())
> +		return NULL;
> +
> +	inode = vma->vm_file->f_path.dentry->d_inode;
> +	mapping = vma->vm_file->f_mapping;
> +	if (pte_none(ptent))
> +		pgoff = linear_page_index(vma, addr);
> +	if (pte_file(ptent))
> +		pgoff = pte_to_pgoff(ptent);
> +
> +	/* page is moved even if it's not RSS of this task(page-faulted). */
> +	if (!mapping_cap_swap_backed(mapping)) { /* normal file */
> +		page = find_get_page(mapping, pgoff);
> +	} else { /* shmem/tmpfs file. we should take account of swap too. */
> +		swp_entry_t ent;
> +		mem_cgroup_get_shmem_target(inode, pgoff, &page, &ent);
> +		if (do_swap_account)
> +			entry->val = ent.val;
> +	}
> +
> +	return page;
> +}

mm/memcontrol.c: In function 'is_target_pte_for_mc':
mm/memcontrol.c:4247: warning: 'pgoff' may be used uninitialized in this function

Either this is a real bug, or we can do

--- a/mm/memcontrol.c~a
+++ a/mm/memcontrol.c
@@ -4255,7 +4255,7 @@ static struct page *mc_handle_file_pte(s
 	mapping = vma->vm_file->f_mapping;
 	if (pte_none(ptent))
 		pgoff = linear_page_index(vma, addr);
-	if (pte_file(ptent))
+	else /* pte_file(ptent) is true */
 		pgoff = pte_to_pgoff(ptent);
 
 	/* page is moved even if it's not RSS of this task(page-faulted). */
_

??

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