linux-kernel - Re: [PATCH 3/3] hugetlbfs: remove unnecessary code after i_mmap

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Message-Id: <b6d50644-7d0c-2c1e-2781-2c6cc81ddc80@linux.ibm.com>
Date:   Mon, 17 Dec 2018 16:04:15 +0530
From:   "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
To:     Mike Kravetz <mike.kravetz@...cle.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Cc:     Michal Hocko <mhocko@...nel.org>, Hugh Dickins <hughd@...gle.com>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.vnet.ibm.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Prakash Sangappa <prakash.sangappa@...cle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        stable@...r.kernel.org
Subject: Re: [PATCH 3/3] hugetlbfs: remove unnecessary code after i_mmap_rwsem
 synchronization

On 12/4/18 1:38 AM, Mike Kravetz wrote:
> After expanding i_mmap_rwsem use for better shared pmd and page fault/
> truncation synchronization, remove code that is no longer necessary.
> 
> Cc: <stable@...r.kernel.org>
> Fixes: ebed4bfc8da8 ("hugetlb: fix absurd HugePages_Rsvd")
> Signed-off-by: Mike Kravetz <mike.kravetz@...cle.com>
> ---
>   fs/hugetlbfs/inode.c | 46 +++++++++++++++-----------------------------
>   mm/hugetlb.c         | 21 ++++++++++----------
>   2 files changed, 25 insertions(+), 42 deletions(-)
> 
> diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
> index 3244147fc42b..a9c00c6ef80d 100644
> --- a/fs/hugetlbfs/inode.c
> +++ b/fs/hugetlbfs/inode.c
> @@ -383,17 +383,16 @@ hugetlb_vmdelete_list(struct rb_root_cached *root, pgoff_t start, pgoff_t end)
>    * truncation is indicated by end of range being LLONG_MAX
>    *	In this case, we first scan the range and release found pages.
>    *	After releasing pages, hugetlb_unreserve_pages cleans up region/reserv
> - *	maps and global counts.  Page faults can not race with truncation
> - *	in this routine.  hugetlb_no_page() prevents page faults in the
> - *	truncated range.  It checks i_size before allocation, and again after
> - *	with the page table lock for the page held.  The same lock must be
> - *	acquired to unmap a page.
> + *	maps and global counts.
>    * hole punch is indicated if end is not LLONG_MAX
>    *	In the hole punch case we scan the range and release found pages.
>    *	Only when releasing a page is the associated region/reserv map
>    *	deleted.  The region/reserv map for ranges without associated
> - *	pages are not modified.  Page faults can race with hole punch.
> - *	This is indicated if we find a mapped page.
> + *	pages are not modified.
> + *
> + * Callers of this routine must hold the i_mmap_rwsem in write mode to prevent
> + * races with page faults.

Should this patch be merged to the previous one? Because the changes to 
callers are done in the previous patch.


> + *
>    * Note: If the passed end of range value is beyond the end of file, but
>    * not LLONG_MAX this routine still performs a hole punch operation.
>    */
> @@ -423,32 +422,14 @@ static void remove_inode_hugepages(struct inode *inode, loff_t lstart,
> 
>   		for (i = 0; i < pagevec_count(&pvec); ++i) {
> 
-aneesh