linux-kernel - Re: [PATCH -v6 2/2] Updating ctime and mtime for memory-mapped files

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Date:	Fri, 18 Jan 2008 12:23:58 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	salikhmetov@...il.com, linux-mm@...ck.org, jakob@...hought.net,
	linux-kernel@...r.kernel.org, valdis.kletnieks@...edu,
	riel@...hat.com, ksm@...dk, staubach@...hat.com,
	jesper.juhl@...il.com, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, protasnb@...il.com,
	r.e.wolff@...wizard.nl, hidave.darkstar@...il.com,
	hch@...radead.org
Subject: Re: [PATCH -v6 2/2] Updating ctime and mtime for memory-mapped
	files


On Fri, 2008-01-18 at 12:17 +0100, Miklos Szeredi wrote:
> > diff --git a/mm/msync.c b/mm/msync.c
> > index 144a757..a1b3fc6 100644
> > --- a/mm/msync.c
> > +++ b/mm/msync.c
> > @@ -14,6 +14,122 @@
> >  #include <linux/syscalls.h>
> >  #include <linux/sched.h>
> >  
> > +unsigned long masync_pte_range(struct vm_area_struct *vma, pmd_t *pdm,
> > +		unsigned long addr, unsigned long end)
> > +{
> > +	pte_t *pte;
> > +	spinlock_t *ptl;
> > +
> > +	pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
> > +	arch_enter_lazy_mmu_mode();
> > +	do {
> > +		pte_t ptent = *pte;
> > +
> > +		if (pte_none(ptent))
> > +			continue;
> > +
> > +		if (!pte_present(ptent))
> > +			continue;
> > +
> > +		if (pte_dirty(ptent) && pte_write(ptent)) {
> > +			flush_cache_page(vma, addr, pte_pfn(ptent));
> 
> Hmm, I'm not sure flush_cache_page() is needed.  Or does does dirty
> data in the cache somehow interfere with the page protection?

No, just being paranoid..

> > +			ptent = ptep_clear_flush(vma, addr, pte);
> > +			ptent = pte_wrprotect(ptent);
> > +			set_pte_at(vma->vm_mnm, addr, pte, ptent);
> > +		}
> > +	} while (pte++, addr += PAGE_SIZE, addr != end);
> > +	arch_leave_lazy_mmu_mode();
> > +	pte_unmap_unlock(pte - 1, ptl);
> > +
> > +	return addr;
> > +}
> > +
> > +unsigned long masync_pmd_range(struct vm_area_struct *vma, pud_t *pud,
> > +		unsigned long addr, unsigned long end)
> > +{
> > +	pmd_t *pmd;
> > +	unsigned long next;
> > +
> > +	pmd = pmd_offset(pud, addr);
> > +	do {
> > +		next = pmd_addr_end(addr, end);
> > +		if (pmd_none_or_clear_bad(pmd))
> > +			continue;
> > +		next = masync_pte_range(vma, pmd, addr, next);
> > +	} while (pmd++, addr = next, addr != end);
> > +
> > +	return addr;
> > +}
> > +
> > +unsigned long masync_pud_range(struct vm_area_struct *vma, pgd_t *pgd,
> > +	       	unsigned long addr, unsigned long end)
> > +{
> > +	pud_t *pud;
> > +	unsigned long next;
> > +
> > +	pud = pud_offset(pgd, addr);
> > +	do {
> > +		next = pud_addr_end(addr, end);
> > +		if (pud_none_or_clear_bad(pud))
> > +			continue;
> > +		next = masync_pmd_range(vma, pud, addr, next);
> > +	} while (pud++, addr = next, addr != end);
> > +
> > +	return addr;
> > +}
> > +
> > +unsigned long masync_pgd_range()
> > +{
> > +	pgd_t *pgd;
> > +	unsigned long next;
> > +
> > +	pgd = pgd_offset(vma->vm_mm, addr);
> > +	do {
> > +		next = pgd_addr_end(addr, end);
> > +		if (pgd_none_of_clear_bad(pgd))
> > +			continue;
> > +		next = masync_pud_range(vma, pgd, addr, next);
> > +	} while (pgd++, addr = next, addr != end);
> > +
> > +	return addr;
> > +}
> > +
> > +int masync_vma_one(struct vm_area_struct *vma,
> > +		unsigned long start, unsigned long end)
> > +{
> > +	if (start < vma->vm_start)
> > +		start = vma->vm_start;
> > +
> > +	if (end > vma->vm_end)
> > +		end = vma->vm_end;
> > +
> > +	masync_pgd_range(vma, start, end);
> > +
> > +	return 0;
> > +}
> > +
> > +int masync_vma(struct vm_area_struct *vma, 
> > +		unsigned long start, unsigned long end)
> > +{
> > +	struct address_space *mapping;
> > +	struct vm_area_struct *vma_iter;
> > +
> > +	if (!(vma->vm_flags & VM_SHARED))
> > +		return 0;
> > +
> > +	mapping = vma->vm_file->f_mapping;
> > +
> > +	if (!mapping_cap_account_dirty(mapping))
> > +		return 0;
> > +
> > +	spin_lock(&mapping->i_mmap_lock);
> > +	vma_prio_tree_foreach(vma_iter, &iter, &mapping->i_mmap, start, end)
> > +		masync_vma_one(vma_iter, start, end);
> > +	spin_unlock(&mapping->i_mmap_lock);
> 
> This is hoding i_mmap_lock for possibly quite long.  Isn't that going
> to cause problems?

Possibly, I didn't see a quick way to break that iteration.
>>From a quick glance at prio_tree.c the iterator isn't valid anymore
after releasing i_mmap_lock. Fixing that would be,.. 'fun'.

I also realized I forgot to copy/paste the prio_tree_iter declaration
and ought to make all these functions static.

But for a quick draft it conveys the idea pretty well, I guess :-)

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