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SubjectRe: [PATCH -V2 0/9] memcg: add HugeTLB resource tracking
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On Mon, 5 Mar 2012 21:56:50 +0800, Hillf Danton <dhillf@gmail.com> wrote:
> On Mon, Mar 5, 2012 at 3:15 AM, Aneesh Kumar K.V
> <aneesh.kumar@linux.vnet.ibm.com> wrote:
> > On Thu, 1 Mar 2012 14:40:29 -0800, Andrew Morton <akpm@linux-foundation.org> wrote:
> >> I haven't begin to get my head around this yet, but I'd like to draw
> >> your attention to https://lkml.org/lkml/2012/2/15/548.
> >
> > Hmm that's really serious bug.
> >
> >>  That fix has
> >> been hanging around for a while, but I haven't done anything with it
> >> yet because I don't like its additional blurring of the separation
> >> between hugetlb core code and hugetlbfs.  I want to find time to sit
> >> down and see if the fix can be better architected but haven't got
> >> around to that yet.
> >>
> >> I expect that your patches will conflict at least mechanically with
> >> David's, which is not a big issue.  But I wonder whether your patches
> >> will copy the same bug into other places, and whether you can think of
> >> a tidier way of addressing the bug which David is seeing?
> >>
> >
> > I will go through the implementation again and make sure the problem
> > explained by David doesn't happen in the new code path added by the
> > patch series.
> >
> Hi Aneesh
>
> When you tackle that problem, please take the following approach also
> into account, though it is a draft, in which quota handback is simply
> eliminated when huge page is freed, if that problem is caused by extra
> reference count.
> And get_quota is carefully paired with put_quota for newly allocated
> page. That is all, and feel free to correct me.

But we should not do put quota until the page is added back to the free pool
right ? otherwise quota subsystem (the actual hugetlb pool) will
indicate availability where as the file system won't have any free
pages.

-aneesh

>
> Best Regards
> -hd
>
> --- a/mm/hugetlb.c Mon Mar 5 20:20:34 2012
> +++ b/mm/hugetlb.c Mon Mar 5 21:20:14 2012
> @@ -533,9 +533,7 @@ static void free_huge_page(struct page *
> */
> struct hstate *h = page_hstate(page);
> int nid = page_to_nid(page);
> - struct address_space *mapping;
>
> - mapping = (struct address_space *) page_private(page);
> set_page_private(page, 0);
> page->mapping = NULL;
> BUG_ON(page_count(page));
> @@ -551,8 +549,6 @@ static void free_huge_page(struct page *
> enqueue_huge_page(h, page);
> }
> spin_unlock(&hugetlb_lock);
> - if (mapping)
> - hugetlb_put_quota(mapping, 1);
> }
>
> static void prep_new_huge_page(struct hstate *h, struct page *page, int nid)
> @@ -1021,7 +1017,8 @@ static void vma_commit_reservation(struc
> }
>
> static struct page *alloc_huge_page(struct vm_area_struct *vma,
> - unsigned long addr, int avoid_reserve)
> + unsigned long addr, int avoid_reserve,
> + long *quota)
> {
> struct hstate *h = hstate_vma(vma);
> struct page *page;
> @@ -1050,7 +1047,8 @@ static struct page *alloc_huge_page(stru
> if (!page) {
> page = alloc_buddy_huge_page(h, NUMA_NO_NODE);
> if (!page) {
> - hugetlb_put_quota(inode->i_mapping, chg);
> + if (chg)
> + hugetlb_put_quota(inode->i_mapping, chg);
> return ERR_PTR(-VM_FAULT_SIGBUS);
> }
> }
> @@ -1058,6 +1056,8 @@ static struct page *alloc_huge_page(stru
> set_page_private(page, (unsigned long) mapping);
>
> vma_commit_reservation(h, vma, addr);
> + if (quota)
> + *quota = chg;
>
> return page;
> }
> @@ -2365,6 +2365,7 @@ static int hugetlb_cow(struct mm_struct
> struct page *old_page, *new_page;
> int avoidcopy;
> int outside_reserve = 0;
> + long quota = 0;
>
> old_page = pte_page(pte);
>
> @@ -2397,7 +2398,8 @@ retry_avoidcopy:
>
> /* Drop page_table_lock as buddy allocator may be called */
> spin_unlock(&mm->page_table_lock);
> - new_page = alloc_huge_page(vma, address, outside_reserve);
> + quota = 0;
> + new_page = alloc_huge_page(vma, address, outside_reserve, &quota);
>
> if (IS_ERR(new_page)) {
> page_cache_release(old_page);
> @@ -2439,6 +2441,8 @@ retry_avoidcopy:
> if (unlikely(anon_vma_prepare(vma))) {
> page_cache_release(new_page);
> page_cache_release(old_page);
> + if (quota)
> + hugetlb_put_quota(vma->vm_file->f_mapping, quota);
> /* Caller expects lock to be held */
> spin_lock(&mm->page_table_lock);
> return VM_FAULT_OOM;
> @@ -2470,6 +2474,8 @@ retry_avoidcopy:
> address & huge_page_mask(h),
> (address & huge_page_mask(h)) + huge_page_size(h));
> }
> + else if (quota)
> + hugetlb_put_quota(vma->vm_file->f_mapping, quota);
> page_cache_release(new_page);
> page_cache_release(old_page);
> return 0;
> @@ -2519,6 +2525,7 @@ static int hugetlb_no_page(struct mm_str
> struct page *page;
> struct address_space *mapping;
> pte_t new_pte;
> + long quota = 0;
>
> /*
> * Currently, we are forced to kill the process in the event the
> @@ -2540,12 +2547,13 @@ static int hugetlb_no_page(struct mm_str
> * before we get page_table_lock.
> */
> retry:
> + quota = 0;
> page = find_lock_page(mapping, idx);
> if (!page) {
> size = i_size_read(mapping->host) >> huge_page_shift(h);
> if (idx >= size)
> goto out;
> - page = alloc_huge_page(vma, address, 0);
> + page = alloc_huge_page(vma, address, 0, &quota);
> if (IS_ERR(page)) {
> ret = -PTR_ERR(page);
> goto out;
> @@ -2560,6 +2568,8 @@ retry:
> err = add_to_page_cache(page, mapping, idx, GFP_KERNEL);
> if (err) {
> put_page(page);
> + if (quota)
> + hugetlb_put_quota(mapping, quota);
> if (err == -EEXIST)
> goto retry;
> goto out;
> @@ -2633,6 +2643,8 @@ backout:
> backout_unlocked:
> unlock_page(page);
> put_page(page);
> + if (quota)
> + hugetlb_put_quota(mapping, quota);
> goto out;
> }
>
> --
>

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