linux-kernel - Re: [PATCH] mm/gup: Allow real explicit breaking of COW

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Message-ID: <20200810145303.GA16451@xz-x1>
Date:   Mon, 10 Aug 2020 10:53:03 -0400
From:   Peter Xu <peterx@...hat.com>
To:     Christoph Hellwig <hch@....de>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Marty Mcfadden <mcfadden8@...l.gov>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jann Horn <jannh@...gle.com>, Oleg Nesterov <oleg@...hat.com>,
        Kirill Shutemov <kirill@...temov.name>, Jan Kara <jack@...e.cz>
Subject: Re: [PATCH] mm/gup: Allow real explicit breaking of COW

On Mon, Aug 10, 2020 at 02:24:19PM +0200, Christoph Hellwig wrote:
> This patch only seems to add a flag, but no actual user of it.

Oops, right.. I'll repost with below squashed into it:

diff --git a/mm/gup.c b/mm/gup.c
index 6f47697f8fb0..9d1f44b01165 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -870,6 +870,8 @@ static int faultin_page(struct task_struct *tsk, struct vm_area_struct *vma,
                return -ENOENT;
        if (*flags & FOLL_WRITE)
                fault_flags |= FAULT_FLAG_WRITE;
+       if (*flags & FOLL_BREAK_COW)
+               fault_flags |= FAULT_FLAG_BREAK_COW;
        if (*flags & FOLL_REMOTE)
                fault_flags |= FAULT_FLAG_REMOTE;
        if (locked)

Thanks,

-- 
Peter Xu