linux-kernel - Re: [PATCH v8 05/22] Add vm_replace

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Message-ID: <20140723142745.GD6754@linux.intel.com>
Date:	Wed, 23 Jul 2014 10:27:45 -0400
From:	Matthew Wilcox <willy@...ux.intel.com>
To:	"Kirill A. Shutemov" <kirill@...temov.name>
Cc:	Matthew Wilcox <matthew.r.wilcox@...el.com>,
	linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 05/22] Add vm_replace_mixed()

On Wed, Jul 23, 2014 at 05:20:48PM +0300, Kirill A. Shutemov wrote:
> On Wed, Jul 23, 2014 at 09:52:22AM -0400, Matthew Wilcox wrote:
> > I'd love to use a lighter-weight weapon!  What would you recommend using,
> > zap_pte_range()?
> 
> The most straight-forward way: extract body of pte cycle from
> zap_pte_range() to separate function -- zap_pte() -- and use it.

OK, I can do that.  What about the other parts of zap_page_range(),
do I need to call them?

        lru_add_drain();
        tlb_gather_mmu(&tlb, mm, address, end);
        update_hiwater_rss(mm);
        mmu_notifier_invalidate_range_start(mm, address, end);
[       unmap_single_vma(&tlb, vma, address, end, details);]
        mmu_notifier_invalidate_range_end(mm, address, end);
        tlb_finish_mmu(&tlb, address, end);

> > 	if ((fd = open(argv[1], O_CREAT|O_RDWR, 0666)) < 0) {
> > 		perror(argv[1]);
> > 		exit(1);
> > 	}
> > 
> > 	if (ftruncate(fd, 4096) < 0) {
> 
> Shouldn't this be ftruncate(fd, 0)? Otherwise the memcpy() below will
> fault in page from backing storage, not hole and write will not replace
> anything.

Ah, it was starting with a new file, hence the O_CREAT up above.

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