linux-kernel - Re: [RFC] remove unnecessary condition in remove_inode

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Date:   Fri, 23 Sep 2016 10:18:17 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     zhong jiang <zhongjiang@...wei.com>
Cc:     Mike Kravetz <mike.kravetz@...cle.com>,
        David Rientjes <rientjes@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Hugh Dickins <hughd@...gle.com>,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Subject: Re: [RFC] remove unnecessary condition in remove_inode_hugepages

[CC Naoya]

On Fri 23-09-16 09:53:52, zhong jiang wrote:
> 
> At present, we need to call hugetlb_fix_reserve_count when hugetlb_unrserve_pages fails,
> and PagePrivate will decide hugetlb reserves counts.
> 
> we obtain the page from page cache. and use page both lock_page and mutex_lock.
> alloc_huge_page add page to page chace always hold lock page, then bail out clearpageprivate
> before unlock page. 
> 
> but I' m not sure  it is right  or I miss the points.
> 
> 
> diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
> index 4ea71eb..010723b 100644
> --- a/fs/hugetlbfs/inode.c
> +++ b/fs/hugetlbfs/inode.c
> @@ -462,14 +462,12 @@ static void remove_inode_hugepages(struct inode *inode, loff_t lstart,
>                          * the page, note PagePrivate which is used in case
>                          * of error.
>                          */
> -                       rsv_on_error = !PagePrivate(page);
>                         remove_huge_page(page);
>                         freed++;
>                         if (!truncate_op) {
>                                 if (unlikely(hugetlb_unreserve_pages(inode,
>                                                         next, next + 1, 1)))
> -                                       hugetlb_fix_reserve_counts(inode,
> -                                                               rsv_on_error);
> +                                       hugetlb_fix_reserve_counts(inode)
>                         }
> 
>                         unlock_page(page);
> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> index c26d463..d2e0fc5 100644
> --- a/include/linux/hugetlb.h
> +++ b/include/linux/hugetlb.h
> @@ -90,7 +90,7 @@ int dequeue_hwpoisoned_huge_page(struct page *page);
>  bool isolate_huge_page(struct page *page, struct list_head *list);
>  void putback_active_hugepage(struct page *page);
>  void free_huge_page(struct page *page);
> -void hugetlb_fix_reserve_counts(struct inode *inode, bool restore_reserve);
> +void hugetlb_fix_reserve_counts(struct inode *inode);
>  extern struct mutex *hugetlb_fault_mutex_table;
>  u32 hugetlb_fault_mutex_hash(struct hstate *h, struct mm_struct *mm,
>                                 struct vm_area_struct *vma,
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 87e11d8..28a079a 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -567,13 +567,13 @@ retry:
>   * appear as a "reserved" entry instead of simply dangling with incorrect
>   * counts.
>   */
> -void hugetlb_fix_reserve_counts(struct inode *inode, bool restore_reserve)
> +void hugetlb_fix_reserve_counts(struct inode *inode)
>  {
>         struct hugepage_subpool *spool = subpool_inode(inode);
>         long rsv_adjust;
> 
>         rsv_adjust = hugepage_subpool_get_pages(spool, 1);
> -       if (restore_reserve && rsv_adjust) {
> +       if (rsv_adjust) {
>                 struct hstate *h = hstate_inode(inode);
> 
>                 hugetlb_acct_memory(h, 1);
> 
> 
> --
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-- 
Michal Hocko
SUSE Labs