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SubjectRe: [PATCH/stylefix 3/4] memcg: avoid account not-on-LRU pages
KAMEZAWA Hiroyuki wrote:
> This is conding-style fixed version. Thank you, Nishimura-san.
> -Kmae
> ==
> There are not-on-LRU pages which can be mapped and they are not worth to
> be accounted. (becasue we can't shrink them and need dirty codes to handle
> specical case) We'd like to make use of usual objrmap/radix-tree's protcol
> and don't want to account out-of-vm's control pages.
>
> When special_mapping_fault() is called, page->mapping is tend to be NULL
> and it's charged as Anonymous page.
> insert_page() also handles some special pages from drivers.
>
> This patch is for avoiding to account special pages.
>
> Changlog: v5 -> v6
> - modified Documentation.
> - fixed to charge only when a page is newly allocated.
>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
>

[snip]
> @@ -2463,6 +2457,7 @@ static int __do_fault(struct mm_struct *
> struct page *page;
> pte_t entry;
> int anon = 0;
> + int charged = 0;
> struct page *dirty_page = NULL;
> struct vm_fault vmf;
> int ret;
> @@ -2503,6 +2498,12 @@ static int __do_fault(struct mm_struct *
> ret = VM_FAULT_OOM;
> goto out;
> }
> + if (mem_cgroup_charge(page, mm, GFP_KERNEL)) {
> + ret = VM_FAULT_OOM;
> + page_cache_release(page);
> + goto out;
> + }
> + charged = 1;

If I understand this correctly, we now account only when the VMA is not shared?
Seems reasonable, since we don't allocate a page otherwise.


[snip]


> Index: mmotm-2.6.27-rc7+/mm/rmap.c
> ===================================================================
> --- mmotm-2.6.27-rc7+.orig/mm/rmap.c
> +++ mmotm-2.6.27-rc7+/mm/rmap.c
> @@ -725,8 +725,8 @@ void page_remove_rmap(struct page *page,
> page_clear_dirty(page);
> set_page_dirty(page);
> }
> -
> - mem_cgroup_uncharge_page(page);
> + if (PageAnon(page))
> + mem_cgroup_uncharge_page(page);

Is the change because we expect the page to get directly uncharged when it is
removed from cache? i.e, page->mapping is set to NULL before uncharge?

Looks good to me, I am yet to test it though.

Acked-by: Balbir Singh <balbir@linux.vnet.ibm.com>


--
Balbir


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