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Subject: Re: [PATCH] mm/mremap: Don't account pages in vma_to_resize()
To:     Dmitry Safonov <dima@arista.com>, linux-kernel@vger.kernel.org
Cc:     Alexander Viro <viro@zeniv.linux.org.uk>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andy Lutomirski <luto@kernel.org>,
        Brian Geffon <bgeffon@google.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Chen Wandun <chenwandun@huawei.com>,
        Dan Carpenter <dan.carpenter@oracle.com>,
        Dan Williams <dan.j.williams@intel.com>,
        Dave Jiang <dave.jiang@intel.com>,
        Hugh Dickins <hughd@google.com>,
        Ingo Molnar <mingo@redhat.com>, Jason Gunthorpe <jgg@ziepe.ca>,
        John Hubbard <jhubbard@nvidia.com>,
        Kefeng Wang <wangkefeng.wang@huawei.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Minchan Kim <minchan@kernel.org>,
        Ralph Campbell <rcampbell@nvidia.com>,
        Russell King <linux@armlinux.org.uk>,
        Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        Thomas Gleixner <tglx@linutronix.de>,
        Vishal Verma <vishal.l.verma@intel.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Wei Yongjun <weiyongjun1@huawei.com>,
        Will Deacon <will@kernel.org>
References: <20210721124949.517217-1-dima@arista.com>
From:   Dmitry Safonov <0x7f454c46@gmail.com>
Message-ID: <cd8fd36b-eba7-039b-f823-f62d62c503b8@gmail.com>
Date:   Wed, 21 Jul 2021 14:08:55 +0100
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On 7/21/21 1:49 PM, Dmitry Safonov wrote:
> All this vm_unacct_memory(charged) dance seems to complicate the life
> without a good reason. Furthermore, it seems not always done right on
> error-pathes in mremap_to().
> And worse than that: this `charged' difference is sometimes
> double-accounted for growing MREMAP_DONTUNMAP mremap()s in move_vma():
> : if (security_vm_enough_memory_mm(mm, new_len >> PAGE_SHIFT))
> 
> Let's not do this.
> Account memory in mremap() fast-path for growing VMAs or in move_vma()
> for actually moving things.

And this one is also wrong: the diff for growing vma should be accounted
for !MREMAP_DONTUNMAP too.
Sending v2...

Thanks,
          Dmitry