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

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Message-ID: <20220412192821.xliop57sblvjx4t4@box.shutemov.name>
Date:   Tue, 12 Apr 2022 22:28:21 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Chao Peng <chao.p.peng@...ux.intel.com>
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 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? 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.

-- 
 Kirill A. Shutemov