lkml.org 
[lkml]   [2008]   [Jan]   [18]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    SubjectRe: [PATCH -v6 2/2] Updating ctime and mtime for memory-mapped files
    From
    Date
    > Updating file times at write references to memory-mapped files and
    > forcing file times update at the next write reference after
    > calling the msync() system call with the MS_ASYNC flag.
    >
    > Signed-off-by: Anton Salikhmetov <salikhmetov@gmail.com>
    > ---
    > mm/memory.c | 6 ++++++
    > mm/msync.c | 52 +++++++++++++++++++++++++++++++++++++++-------------
    > 2 files changed, 45 insertions(+), 13 deletions(-)
    >
    > diff --git a/mm/memory.c b/mm/memory.c
    > index 4bf0b6d..13d5bbf 100644
    > --- a/mm/memory.c
    > +++ b/mm/memory.c
    > @@ -1668,6 +1668,9 @@ gotten:
    > unlock:
    > pte_unmap_unlock(page_table, ptl);
    > if (dirty_page) {
    > + if (vma->vm_file)
    > + file_update_time(vma->vm_file);
    > +
    > /*
    > * Yes, Virginia, this is actually required to prevent a race
    > * with clear_page_dirty_for_io() from clearing the page dirty
    > @@ -2341,6 +2344,9 @@ out_unlocked:
    > if (anon)
    > page_cache_release(vmf.page);
    > else if (dirty_page) {
    > + if (vma->vm_file)
    > + file_update_time(vma->vm_file);
    > +
    > set_page_dirty_balance(dirty_page, page_mkwrite);
    > put_page(dirty_page);
    > }
    > 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).

    > +
    > +/*
    > * MS_SYNC syncs the entire file - including mappings.
    > *
    > - * MS_ASYNC does not start I/O (it used to, up to 2.5.67).
    > - * Nor does it mark the relevant pages dirty (it used to up to 2.6.17).
    > - * Now it doesn't do anything, since dirty pages are properly tracked.
    > + * MS_ASYNC does not start I/O. Instead, it marks the relevant pages
    > + * read-only by calling vma_wrprotect(). This is needed to catch the next
    > + * write reference to the mapped region and update the file times
    > + * accordingly.
    > *
    > * The application may now run fsync() to write out the dirty pages and
    > * wait on the writeout and check the result. Or the application may run
    > @@ -77,16 +99,20 @@ asmlinkage long sys_msync(unsigned long start, size_t len, int flags)
    > error = 0;
    > start = vma->vm_end;
    > file = vma->vm_file;
    > - if (file && (vma->vm_flags & VM_SHARED) && (flags & MS_SYNC)) {
    > - get_file(file);
    > - up_read(&mm->mmap_sem);
    > - error = do_fsync(file, 0);
    > - fput(file);
    > - if (error || start >= end)
    > - goto out;
    > - down_read(&mm->mmap_sem);
    > - vma = find_vma(mm, start);
    > - continue;
    > + if (file && (vma->vm_flags & VM_SHARED)) {
    > + if (flags & MS_ASYNC)
    > + vma_wrprotect(vma);
    > + if (flags & MS_SYNC) {
    > + get_file(file);
    > + up_read(&mm->mmap_sem);
    > + error = do_fsync(file, 0);
    > + fput(file);
    > + if (error || start >= end)
    > + goto out;
    > + down_read(&mm->mmap_sem);
    > + vma = find_vma(mm, start);
    > + continue;
    > + }
    > }
    >
    > vma = vma->vm_next;
    > --
    > 1.4.4.4
    >
    >


    \
     
     \ /
      Last update: 2008-01-18 10:53    [W:0.029 / U:1.076 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site