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

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Message-ID: <cd8fd36b-eba7-039b-f823-f62d62c503b8@gmail.com>
Date:   Wed, 21 Jul 2021 14:08:55 +0100
From:   Dmitry Safonov <0x7f454c46@...il.com>
To:     Dmitry Safonov <dima@...sta.com>, linux-kernel@...r.kernel.org
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Brian Geffon <bgeffon@...gle.com>,
        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] mm/mremap: Don't account pages in vma_to_resize()

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