linux-kernel - Re: [PATCH v2 7/7] mm/mremap: thread state through move page table operation

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Message-ID: <0602cc1a-0013-47ec-9111-1b4fdf8f44ae@lucifer.local>
Date: Mon, 10 Mar 2025 18:13:59 +0000
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
        "Liam R . Howlett" <Liam.Howlett@...cle.com>,
        Jann Horn <jannh@...gle.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Harry Yoo <harry.yoo@...cle.com>,
        Yosry Ahmed <yosry.ahmed@...ux.dev>
Subject: Re: [PATCH v2 7/7] mm/mremap: thread state through move page table
 operation

On Mon, Mar 10, 2025 at 06:52:25PM +0100, Vlastimil Babka wrote:
> On 3/6/25 11:34, Lorenzo Stoakes wrote:
> > Finish refactoring the page table logic by threading the PMC state
> > throughout the operation, allowing us to control the operation as we go.
> >
> > Additionally, update the old_addr, new_addr fields in move_page_tables()
> > as we progress through the process making use of the fact we have this
> > state object now to track this.
> >
> > With these changes made, not only is the code far more readable, but we
> > can finally transmit state throughout the entire operation, which lays the
> > groundwork for sensibly making changes in future to how the mremap()
> > operation is performed.
> >
> > Additionally take the opportunity to refactor the means of determining the
> > progress of the operation, abstracting this to pmc_progress() and
> > simplifying the logic to make it clearer what's going on.
> >
> > Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
>
> Reviewed-by: Vlastimil Babka <vbabka@...e.cz>

Thanks!

>
> Small nit:
>
> >
> > +/*
> > + * Should move_pgt_entry() acquire the rmap locks? This is either expressed in
> > + * the PMC, or overridden in the case of normal, larger page tables.
> > + */
> > +static bool should_take_rmap_locks(struct pagetable_move_control *pmc,
> > +				   enum pgt_entry entry)
> > +{
> > +	if (pmc->need_rmap_locks)
> > +		return true;
> > +
> > +	switch (entry) {
> > +	case NORMAL_PMD:
> > +	case NORMAL_PUD:
> > +		return true;
> > +	default:
> > +		return false;
> > +	}
> > +}
> > +
>
> IMHO the "overriden" logic would be more obvious if we removed the initial
> "if" and just had default: return pmc->need_rmap_locks

Ack, agreed, will fix!