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Message-Id: <1200654050.5920.14.camel@twins>
Date: Fri, 18 Jan 2008 12:00:50 +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 11:38 +0100, Miklos Szeredi wrote:
> > On Fri, 2008-01-18 at 10:51 +0100, Miklos Szeredi wrote:
> >
> > > > diff --git a/mm/msync.c b/mm/msync.c
> > > > index a4de868..a49af28 100644
> > > > --- a/mm/msync.c
> > > > +++ b/mm/msync.c
> > > > @@ -13,11 +13,33 @@
> > > > #include <linux/syscalls.h>
> > > >
> > > > /*
> > > > + * Scan the PTEs for pages belonging to the VMA and mark them read-only.
> > > > + * It will force a pagefault on the next write access.
> > > > + */
> > > > +static void vma_wrprotect(struct vm_area_struct *vma)
> > > > +{
> > > > + unsigned long addr;
> > > > +
> > > > + for (addr = vma->vm_start; addr < vma->vm_end; addr += PAGE_SIZE) {
> > > > + spinlock_t *ptl;
> > > > + pgd_t *pgd = pgd_offset(vma->vm_mm, addr);
> > > > + pud_t *pud = pud_offset(pgd, addr);
> > > > + pmd_t *pmd = pmd_offset(pud, addr);
> > > > + pte_t *pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
> > > > +
> > > > + if (pte_dirty(*pte) && pte_write(*pte))
> > > > + *pte = pte_wrprotect(*pte);
> > > > + pte_unmap_unlock(pte, ptl);
> > > > + }
> > > > +}
> > >
> > > What about ram based filesystems? They don't start out with read-only
> > > pte's, so I think they don't want them read-protected now either.
> > > Unless this is essential for correct mtime/ctime accounting on these
> > > filesystems (I don't think it really is). But then the mapping should
> > > start out read-only as well, otherwise the time update will only work
> > > after an msync(MS_ASYNC).
> >
> > page_mkclean() has all the needed logic for this, it also walks the rmap
> > and cleans out all other users, which I think is needed too for
> > consistencies sake:
> >
> > Process A Process B
> >
> > mmap(foo.txt) mmap(foo.txt)
> >
> > dirty page
> > dirty page
> >
> > msync(MS_ASYNC)
> >
> > dirty page
> >
> > msync(MS_ASYNC) <--- now what?!
how about:
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));
+ 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);
+
+ return 0;
+}
+
/*
* MS_SYNC syncs the entire file - including mappings.
*
--
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