Reading through the tree, I see that some callers of get_user_pages()
release the pages that they got via put_page(), and some callers use
page_cache_release(). Of course <linux/pagemap.h> has
#define page_cache_release(page) put_page(page)
so this is really not much of a difference, but I'd like to know which
is considered better style. Any opinions?
Thanks,
Roland
Roland Dreier wrote:
> Reading through the tree, I see that some callers of get_user_pages()
> release the pages that they got via put_page(), and some callers use
> page_cache_release(). Of course <linux/pagemap.h> has
>
> #define page_cache_release(page) put_page(page)
>
> so this is really not much of a difference, but I'd like to know which
> is considered better style. Any opinions?
I've defined this function. I'm not sure if it really works, but it
looks good.
#include <linux/pagemap.h>
void put_user_pages(int len, struct page **pages)
{
int i;
for (i=0; i<len; i++) {
if (!PageReserved(pages[i])) {
SetPageDirty(pages[i]);
}
page_cache_release(pages[i]);
}
}
--
Timur Tabi
Staff Software Engineer
[email protected]
Timur Tabi <[email protected]> wrote:
>
> Roland Dreier wrote:
>
> > Reading through the tree, I see that some callers of get_user_pages()
> > release the pages that they got via put_page(), and some callers use
> > page_cache_release(). Of course <linux/pagemap.h> has
> >
> > #define page_cache_release(page) put_page(page)
> >
> > so this is really not much of a difference, but I'd like to know which
> > is considered better style. Any opinions?
I guess we should only use page_cache_release() if the page is known to be
pagecache. In the case of get_user_pages() the page could of course be
anonymous in which case put_page is probably more appropriate. It's all a
bit of a mess and if we ever do end up having PAGE_CACHE_SIZE > PAGE_SIZE,
someone will have some work to do.
I suppose put_page() would be better for now.
> I've defined this function. I'm not sure if it really works, but it
> looks good.
>
> #include <linux/pagemap.h>
>
> void put_user_pages(int len, struct page **pages)
> {
> int i;
>
> for (i=0; i<len; i++) {
> if (!PageReserved(pages[i])) {
> SetPageDirty(pages[i]);
> }
> page_cache_release(pages[i]);
> }
> }
no... You should only dirty the page if it was modified, and then use
set_page_dirty() or set_page_dirty_lock().
See dio_bio_complete() for an example.
Andrew Morton wrote:
> no... You should only dirty the page if it was modified, and then use
> set_page_dirty() or set_page_dirty_lock().
If the page was modified, then shouldn't it already be marked dirty?
Also, should I always use set_page_dirty_lock() if I haven't already
locked the page?
--
Timur Tabi
Staff Software Engineer
[email protected]
Timur Tabi <[email protected]> wrote:
>
> Andrew Morton wrote:
>
> > no... You should only dirty the page if it was modified, and then use
> > set_page_dirty() or set_page_dirty_lock().
>
> If the page was modified, then shouldn't it already be marked dirty?
If the page is modified by a DMA transfer or by the CPU via the kernel's
page mappings then there is no record of its having been altered. Which is
why we must do it in software.
> Also, should I always use set_page_dirty_lock() if I haven't already
> locked the page?
If you don't have a reference on the page's inode, yes, you should use
set_page_dirty_lock(). If the page came from get_user_pages() then surely
you don't have a ref on the inode.