From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lf0-f72.google.com (mail-lf0-f72.google.com [209.85.215.72]) by kanga.kvack.org (Postfix) with ESMTP id 941E2280273 for ; Mon, 26 Sep 2016 16:16:35 -0400 (EDT) Received: by mail-lf0-f72.google.com with SMTP id n4so106987186lfb.3 for ; Mon, 26 Sep 2016 13:16:35 -0700 (PDT) Received: from userp1040.oracle.com (userp1040.oracle.com. [156.151.31.81]) by mx.google.com with ESMTPS id y3si9350383wjm.10.2016.09.26.13.16.33 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 26 Sep 2016 13:16:34 -0700 (PDT) Subject: Re: [PATCH] mm: remove unnecessary condition in remove_inode_hugepages References: <1474857253-35702-1-git-send-email-zhongjiang@huawei.com> <20160926090121.GC28550@dhcp22.suse.cz> From: Mike Kravetz Message-ID: <9d43eafa-a3c2-01c8-53c7-6654ad0114e9@oracle.com> Date: Mon, 26 Sep 2016 13:16:02 -0700 MIME-Version: 1.0 In-Reply-To: <20160926090121.GC28550@dhcp22.suse.cz> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko , zhongjiang Cc: akpm@linux-foundation.org, n-horiguchi@ah.jp.nec.com, linux-mm@kvack.org On 09/26/2016 02:01 AM, Michal Hocko wrote: > On Mon 26-09-16 10:34:13, zhongjiang wrote: >> From: zhong jiang >> >> when the huge page is added to the page cahce (huge_add_to_page_cache), >> the page private flag will be cleared. since this code >> (remove_inode_hugepages) will only be called for pages in the >> page cahce, PagePrivate(page) will always be false. >> >> The patch remove the code without any functional change. >> >> Signed-off-by: zhong jiang >> --- >> fs/hugetlbfs/inode.c | 10 ++++------ >> include/linux/hugetlb.h | 2 +- >> mm/hugetlb.c | 4 ++-- >> 3 files changed, 7 insertions(+), 9 deletions(-) >> >> diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c >> index 4ea71eb..81f8bbf4 100644 >> --- a/fs/hugetlbfs/inode.c >> +++ b/fs/hugetlbfs/inode.c >> @@ -458,18 +458,16 @@ static void remove_inode_hugepages(struct inode *inode, loff_t lstart, >> * cache (remove_huge_page) BEFORE removing the >> * region/reserve map (hugetlb_unreserve_pages). In >> * rare out of memory conditions, removal of the >> - * region/reserve map could fail. Before free'ing >> - * the page, note PagePrivate which is used in case >> - * of error. >> + * region/reserve map could fail. Correspondingly, >> + * the subpool and global reserve usage count can need >> + * to be adjusted. >> */ >> - rsv_on_error = !PagePrivate(page); > > This whole code is tricky as hell. I would be calmer if we just stick a > VM_BUG_ON here to make sure that this assumption will not break later > on. I'm OK with adding the VM_BUG_ON. This has run through the fallocate stress testing without issue. In addition, I ran it through the (in development) userfaultfd huge page tests that use fallocate hole punch on a privately mapped hugetlbfs file. The original check for PagePrivate was likely added due to observations about the way the flag is used in dequeue_huge_page_vma/free_huge_page. Unfortunately, I did not recognize that they did not apply in this case. -- Mike Kravetz > >> 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); >> -- >> 1.8.3.1 > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. 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