Re: [PATCH 1/3] mm/gup: introduce __put_user_pages()

On 7/22/19 10:53 PM, Christoph Hellwig wrote:

On Mon, Jul 22, 2019 at 03:34:13PM -0700, john.hubbard@gmail.com wrote:

quoted

+enum pup_flags_t {
+	PUP_FLAGS_CLEAN		= 0,
+	PUP_FLAGS_DIRTY		= 1,
+	PUP_FLAGS_LOCK		= 2,
+	PUP_FLAGS_DIRTY_LOCK	= 3,
+};

Well, the enum defeats the ease of just being able to pass a boolean
expression to the function, which would simplify a lot of the caller,
so if we need to support the !locked version I'd rather see that as
a separate helper.

But do we actually have callers where not using the _lock version is
not a bug?  set_page_dirty makes sense in the context of a file systems
that have a reference to the inode the page hangs off, but that is
(almost?) never the case for get_user_pages.

I'm seeing about 18 places where set_page_dirty() is used, in the call site
conversions so far, and about 20 places where set_page_dirty_lock() is
used. So without knowing how many of the former (if any) represent bugs,
you can see why the proposal here supports both DIRTY and DIRTY_LOCK.

Anyway, yes, I could change it, based on your estimation that most of the 
set_page_dirty() calls really should be set_page_dirty_lock().
In that case, we would end up with approximately the following:

/* Here, "dirty" really means, "call set_page_dirty_lock()": */
void __put_user_pages(struct page **pages, unsigned long npages,
		      bool dirty);

/* Here, "dirty" really means, "call set_page_dirty()": */
void __put_user_pages_unlocked(struct page **pages, unsigned long npages,
			       bool dirty);

?


thanks,
-- 
John Hubbard
NVIDIA