On Mon 01-12-14 17:58:02, Johannes Weiner wrote:
> Whether there is a vm_ops->page_mkwrite or not, the page dirtying is
> pretty much the same. Make sure the page references are the same in
> both cases, then merge the two branches.
>
> It's tempting to go even further and page-lock the !page_mkwrite case,
> to get it in line with everybody else setting the page table and thus
> further simplify the model. But that's not quite compelling enough to
> justify dropping the pte lock, then relocking and verifying the entry
> for filesystems without ->page_mkwrite, which notably includes tmpfs.
> Leave it for now and lock the page late in the !page_mkwrite case.
>
> Signed-off-by: Johannes Weiner <[email protected]>
> ---
> mm/memory.c | 46 ++++++++++++++++------------------------------
> 1 file changed, 16 insertions(+), 30 deletions(-)
>
> diff --git a/mm/memory.c b/mm/memory.c
> index 2a2e3648ed65..ff92abfa5303 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
...
> @@ -2147,42 +2147,28 @@ reuse:
> pte_unmap_unlock(page_table, ptl);
> ret |= VM_FAULT_WRITE;
>
> - if (!dirty_page)
> - return ret;
> -
> - if (!page_mkwrite) {
> + if (dirty_shared) {
> struct address_space *mapping;
> int dirtied;
>
> - lock_page(dirty_page);
> - dirtied = set_page_dirty(dirty_page);
> - mapping = dirty_page->mapping;
> - unlock_page(dirty_page);
> + if (!page_mkwrite)
> + lock_page(old_page);
>
> - if (dirtied && mapping) {
> - /*
> - * Some device drivers do not set page.mapping
> - * but still dirty their pages
> - */
> - balance_dirty_pages_ratelimited(mapping);
> - }
> + dirtied = set_page_dirty(old_page);
> + mapping = old_page->mapping;
> + unlock_page(old_page);
> + page_cache_release(old_page);
>
> - file_update_time(vma->vm_file);
> - }
> - put_page(dirty_page);
> - if (page_mkwrite) {
> - struct address_space *mapping = dirty_page->mapping;
> -
> - set_page_dirty(dirty_page);
> - unlock_page(dirty_page);
> - page_cache_release(dirty_page);
> - if (mapping) {
> + if ((dirtied || page_mkwrite) && mapping) {
Why do we actually call balance_dirty_pages_ratelimited() even if we
didn't dirty the page when ->page_mkwrite() exists? Is it because
filesystem may dirty the page in ->page_mkwrite() and we don't want it to
deal with calling balance_dirty_pages_ratelimited()?
Otherwise the patch looks good to me.
Honza
> /*
> * Some device drivers do not set page.mapping
> * but still dirty their pages
> */
> balance_dirty_pages_ratelimited(mapping);
> }
> +
> + if (!page_mkwrite)
> + file_update_time(vma->vm_file);
> }
>
> return ret;
> --
> 2.1.3
>
--
Jan Kara <[email protected]>
SUSE Labs, CR
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