From: Peter Xu <peterx@redhat.com>
To: Mike Kravetz <mike.kravetz@oracle.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Kirill Shutemov <kirill@shutemov.name>,
Wei Zhang <wzam@amazon.com>,
Mike Rapoport <rppt@linux.vnet.ibm.com>,
Matthew Wilcox <willy@infradead.org>,
Miaohe Lin <linmiaohe@huawei.com>,
Andrea Arcangeli <aarcange@redhat.com>,
Gal Pressman <galpress@amazon.com>, Jan Kara <jack@suse.cz>,
Jann Horn <jannh@google.com>,
Andrew Morton <akpm@linux-foundation.org>,
Kirill Tkhai <ktkhai@virtuozzo.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Jason Gunthorpe <jgg@ziepe.ca>,
David Gibson <david@gibson.dropbear.id.au>,
Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH v2 4/4] hugetlb: Do early cow when page pinned on src mm
Date: Fri, 5 Feb 2021 11:05:30 -0500 [thread overview]
Message-ID: <20210205160530.GZ6468@xz-x1> (raw)
In-Reply-To: <4344397d-cf08-b502-d5ff-76f19e778dfe@oracle.com>
On Thu, Feb 04, 2021 at 09:11:24PM -0800, Mike Kravetz wrote:
[...]
> >>> @@ -3787,7 +3803,7 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src,
> >>> dst_entry = huge_ptep_get(dst_pte);
> >>> if ((dst_pte == src_pte) || !huge_pte_none(dst_entry))
> >>> continue;
> >>> -
> >>> +again:
> >>> dst_ptl = huge_pte_lock(h, dst, dst_pte);
> >>> src_ptl = huge_pte_lockptr(h, src, src_pte);
> >>> spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING);
> >
> > Side question: Mike, do you know why we need this lock_nested()? Could the src
> > lock be taken due to any reason already? It confused me when I read the chunk.
>
> I see that it was added with commit 4647875819aa. That was when huge pages
> used the single per-mm ptl. Lockdep seemed to complain about taking
> &mm->page_table_lock twice. Certainly, source and destination mm can not
> be the same. Right?
Right, at least that's my understanding..
> I do not have the full history, but it 'looks' like
> lockdep might have been confused and this was added to keep it quiet.
>
> BTW - Copy page range for 'normal' pages has the same spin_lock_nested().
Yes. I'll need to take the same lock in v3, so I think I'll just follow.
Thanks,
--
Peter Xu
next prev parent reply other threads:[~2021-02-05 23:29 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-04 14:50 [PATCH v2 0/4] mm/hugetlb: Early cow on fork, and a few cleanups Peter Xu
2021-02-04 14:50 ` [PATCH v2 1/4] hugetlb: Dedup the code to add a new file_region Peter Xu
2021-02-04 14:50 ` [PATCH v2 2/4] hugetlg: Break earlier in add_reservation_in_range() when we can Peter Xu
2021-02-04 14:50 ` [PATCH v2 3/4] mm: Introduce page_needs_cow_for_dma() for deciding whether cow Peter Xu
2021-02-04 17:54 ` Linus Torvalds
2021-02-04 19:25 ` Peter Xu
2021-02-04 23:20 ` Jason Gunthorpe
2021-02-05 0:50 ` Peter Xu
2021-02-04 14:50 ` [PATCH v2 4/4] hugetlb: Do early cow when page pinned on src mm Peter Xu
2021-02-04 23:25 ` Mike Kravetz
2021-02-05 1:43 ` Peter Xu
2021-02-05 5:11 ` Mike Kravetz
2021-02-05 16:05 ` Peter Xu [this message]
[not found] ` <329ADC08-552E-423B-9230-99643B81C14A@amazon.com>
2021-02-05 15:51 ` Peter Xu
2021-02-07 9:09 ` Gal Pressman
2021-02-07 15:31 ` Peter Xu
2021-02-04 20:20 ` [PATCH v2 5/4] mm: Use is_cow_mapping() across tree where proper Peter Xu
2021-02-04 20:26 ` Linus Torvalds
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