linux-kernel - Re: [PATCH v2] mm/mremap: Don't account pages in vma_to

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Date:   Wed, 21 Jul 2021 21:18:30 +0100
From:   Dmitry Safonov <0x7f454c46@...il.com>
To:     Dmitry Safonov <dima@...sta.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Brian Geffon <bgeffon@...gle.com>
Cc:     linux-kernel@...r.kernel.org,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Andy Lutomirski <luto@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Chen Wandun <chenwandun@...wei.com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Hugh Dickins <hughd@...gle.com>,
        Ingo Molnar <mingo@...hat.com>, Jason Gunthorpe <jgg@...pe.ca>,
        John Hubbard <jhubbard@...dia.com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Minchan Kim <minchan@...nel.org>,
        Ralph Campbell <rcampbell@...dia.com>,
        Russell King <linux@...linux.org.uk>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vishal Verma <vishal.l.verma@...el.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Wei Yongjun <weiyongjun1@...wei.com>,
        Will Deacon <will@...nel.org>
Subject: Re: [PATCH v2] mm/mremap: Don't account pages in vma_to_resize()

On 7/21/21 9:08 PM, Dmitry Safonov wrote:
> On 7/21/21 9:05 PM, Andrew Morton wrote:
>> On Wed, 21 Jul 2021 14:21:54 +0100 Dmitry Safonov <0x7f454c46@...il.com> wrote:
>>
>>>> Let's not do this.
>>>> Account memory in mremap() fast-path for growing VMAs or in move_vma()
>>>> for actually moving things. The same simpler way as it's done by
>>>> vm_stat_account(), but with a difference to call
>>>> security_vm_enough_memory_mm() before copying/adjusting VMA.
>>>>
>>>> Originally noticed by Chen Wandun:
>>>> https://lkml.kernel.org/r/20210717101942.120607-1-chenwandun@huawei.com
>>>
>>> The patch by Chen Wandun still makes sense with this v2.
>>> Heh :-)
>>
>> Should
>> https://lkml.kernel.org/r/20210717101942.120607-1-chenwandun@huawei.com
>> still be applied then?  Did you ack it?
>>
> 
> Yes, please keep that patch with
> Acked-by: Dmitry Safonov <dima@...sta.com>
> 
> This one comes on the top to correct accounting for MREMAP_DONTUNMAP.

Please, also wait for reviews for this one.
I think it's correct and simplifies the complex code, but now I look
into the code again, I see that:
:	/*
:	 * MREMAP_DONTUNMAP is always a move and it does not allow resizing
:	 * in the process.
:	 */
:	if (flags & MREMAP_DONTUNMAP &&
:			(!(flags & MREMAP_MAYMOVE) || old_len != new_len))
:		return ret;

So, this part can be dropped:
> Fixes: e346b3813067 ("mm/mremap: add MREMAP_DONTUNMAP to mremap()")

But I think the patch still makes sense.

Brian, can I have your review on it?

Thanks,
          Dmitry