linux-kernel - Re: [PATCH v5 04/13] mm/shmem: Restrict MFD_INACCESSIBLE memory against RLIMIT

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Date:   Wed, 13 Apr 2022 17:15:33 +0800
From:   Chao Peng <chao.p.peng@...ux.intel.com>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     Sean Christopherson <seanjc@...gle.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org, linux-api@...r.kernel.org,
        qemu-devel@...gnu.org, Paolo Bonzini <pbonzini@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H . Peter Anvin" <hpa@...or.com>,
        Hugh Dickins <hughd@...gle.com>,
        Jeff Layton <jlayton@...nel.org>,
        "J . Bruce Fields" <bfields@...ldses.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Rapoport <rppt@...nel.org>,
        Steven Price <steven.price@....com>,
        "Maciej S . Szmigiero" <mail@...iej.szmigiero.name>,
        Vlastimil Babka <vbabka@...e.cz>,
        Vishal Annapurve <vannapurve@...gle.com>,
        Yu Zhang <yu.c.zhang@...ux.intel.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        luto@...nel.org, jun.nakajima@...el.com, dave.hansen@...el.com,
        ak@...ux.intel.com, david@...hat.com
Subject: Re: [PATCH v5 04/13] mm/shmem: Restrict MFD_INACCESSIBLE memory
 against RLIMIT_MEMLOCK

On Tue, Apr 12, 2022 at 10:28:21PM +0300, Kirill A. Shutemov wrote:
> On Tue, Apr 12, 2022 at 09:39:25PM +0800, Chao Peng wrote:
> > On Mon, Apr 11, 2022 at 06:32:33PM +0300, Kirill A. Shutemov wrote:
> > > On Thu, Apr 07, 2022 at 04:05:36PM +0000, Sean Christopherson wrote:
> > > > Hmm, shmem_writepage() already handles SHM_F_INACCESSIBLE by rejecting the swap, so
> > > > maybe it's just the page migration path that needs to be updated?
> > > 
> > > My early version prevented migration with -ENOTSUPP for
> > > address_space_operations::migratepage().
> > > 
> > > What's wrong with that approach?
> > 
> > I previously thought migratepage will not be called since we already
> > marked the pages as UNMOVABLE, sounds not correct?
> 
> Do you mean missing __GFP_MOVABLE?

Yes.

> I can be wrong, but I don't see that it
> direclty affects if the page is migratable. It is a hint to page allocator
> to group unmovable pages to separate page block and impove availablity of
> higher order pages this way. Page allocator tries to allocate unmovable
> pages from pages blocks that already have unmovable pages.

OK, thanks.

Chao
> 
> -- 
>  Kirill A. Shutemov