linux-kernel - Re: [v1 1/1] xen, mm: Allow deferred page initialization for xen pv domains

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Message-ID: <CAOAebxt6CtQYQ5MxOrpyrLdVapPnw3XePTWUAz1SGuRoukaNGA@mail.gmail.com>
Date:   Mon, 26 Feb 2018 08:39:54 -0500
From:   Pavel Tatashin <pasha.tatashin@...cle.com>
To:     Juergen Gross <jgross@...e.com>
Cc:     Steve Sistare <steven.sistare@...cle.com>,
        Daniel Jordan <daniel.m.jordan@...cle.com>,
        akataria@...are.com, Thomas Gleixner <tglx@...utronix.de>,
        mingo@...hat.com, hpa@...or.com, x86@...nel.org,
        boris.ostrovsky@...cle.com,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Andy Lutomirski <luto@...nel.org>, labbott@...hat.com,
        kirill.shutemov@...ux.intel.com, bp@...e.de,
        minipli@...glemail.com, jinb.park7@...il.com,
        dan.j.williams@...el.com, bhe@...hat.com,
        zhang.jia@...ux.alibaba.com,
        Mel Gorman <mgorman@...hsingularity.net>,
        Johannes Weiner <hannes@...xchg.org>,
        virtualization@...ts.linux-foundation.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        xen-devel@...ts.xenproject.org,
        Linux Memory Management List <linux-mm@...ck.org>
Subject: Re: [v1 1/1] xen, mm: Allow deferred page initialization for xen pv domains

Hi Juergen,

Thank you for taking a look at this patch, I will address your
comments, and send out an updated patch.

>>  extern void default_banner(void);
>>
>> +static inline void paravirt_after_bootmem(void)
>> +{
>> +     pv_init_ops.after_bootmem();
>> +}
>> +
>
> Putting this in the paravirt framework is overkill IMO. There is no need
> to patch the callsites for optimal performance.
>
> I'd put it into struct x86_hyper_init and pre-init it with x86_init_noop

Sure, I will move it into x86_hyper_init.

>>
>> +/*
>> + * During early boot all pages are pinned, but we do not have struct pages,
>> + * so return true until struct pages are ready.
>> + */
>
> Uuh, this comment is just not true.
>
> The "pinned" state for Xen means it is a pv pagetable known to Xen. Such
> pages are read-only for the guest and can be modified via hypercalls
> only.
>
> So either the "pinned" state will be tested for page tables only, in
> which case the comment needs adjustment, or the code is wrong.

The comment should state: During early boot all _page table_ pages are pinned

Thank you,
Pavel