linux-kernel - Re: [RFC 1/7] mm: introduce MADV

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Date:   Tue, 28 May 2019 21:39:27 +0900
From:   Minchan Kim <minchan@...nel.org>
To:     Hillf Danton <hdanton@...a.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>, Michal Hocko <mhocko@...e.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Tim Murray <timmurray@...gle.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Daniel Colascione <dancol@...gle.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Sonny Rao <sonnyrao@...gle.com>,
        Brian Geffon <bgeffon@...gle.com>
Subject: Re: [RFC 1/7] mm: introduce MADV_COOL

On Tue, May 28, 2019 at 08:15:23PM +0800, Hillf Danton wrote:
< snip >
> > > > +
> > > > +			get_page(page);
> > > > +			spin_unlock(ptl);
> > > > +			lock_page(page);
> > > > +			err = split_huge_page(page);
> > > > +			unlock_page(page);
> > > > +			put_page(page);
> > > > +			if (!err)
> > > > +				goto regular_page;
> > > > +			return 0;
> > > > +		}
> > > > +
> > > > +		pmdp_test_and_clear_young(vma, addr, pmd);
> > > > +		deactivate_page(page);
> > > > +huge_unlock:
> > > > +		spin_unlock(ptl);
> > > > +		return 0;
> > > > +	}
> > > > +
> > > > +	if (pmd_trans_unstable(pmd))
> > > > +		return 0;
> > > > +
> > > > +regular_page:
> > >
> > > Take a look at pending signal?
> >
> > Do you have any reason to see pending signal here? I want to know what's
> > your requirement so that what's the better place to handle it.
> >
> We could bail out without work done IMO if there is a fatal siganl pending.
> And we can do that, if it makes sense to you, before the hard work.

Make sense, especically, swapping out.
I will add it in next revision.

> 
> > >
> > > > +	orig_pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
> > > > +	for (pte = orig_pte; addr < end; pte++, addr += PAGE_SIZE) {
> > >
> > > s/end/next/ ?
> >
> > Why do you think it should be next?
> >
> Simply based on the following line, and afraid that next != end
> 	> > > +	next = pmd_addr_end(addr, end);

pmd_addr_end will return smaller address so end is more proper.

> 
> > > > +		ptent = *pte;
> > > > +
> > > > +		if (pte_none(ptent))
> > > > +			continue;
> > > > +
> > > > +		if (!pte_present(ptent))
> > > > +			continue;
> > > > +
> > > > +		page = vm_normal_page(vma, addr, ptent);
> > > > +		if (!page)
> > > > +			continue;
> > > > +
> > > > +		if (page_mapcount(page) > 1)
> > > > +			continue;
> > > > +
> > > > +		ptep_test_and_clear_young(vma, addr, pte);
> > > > +		deactivate_page(page);
> > > > +	}
> > > > +
> > > > +	pte_unmap_unlock(orig_pte, ptl);
> > > > +	cond_resched();
> > > > +
> > > > +	return 0;
> > > > +}
> > > > +
> > > > +static long madvise_cool(struct vm_area_struct *vma,
> > > > +			unsigned long start_addr, unsigned long end_addr)
> > > > +{
> > > > +	struct mm_struct *mm = vma->vm_mm;
> > > > +	struct mmu_gather tlb;
> > > > +
> > > > +	if (vma->vm_flags & (VM_LOCKED|VM_HUGETLB|VM_PFNMAP))
> > > > +		return -EINVAL;
> > >
> > > No service in case of VM_IO?
> >
> > I don't know VM_IO would have regular LRU pages but just follow normal
> > convention for DONTNEED and FREE.
> > Do you have anything in your mind?
> >
> I want to skip a mapping set up for DMA.

What you meant is those pages in VM_IO vma are not in LRU list?
Or
pages in the vma are always pinned so no worth to deactivate or reclaim?