Re: [PATCH 2/2] mm: Use clear_bit_unlock_is_negative_byte for PageWriteback

On Thu 26-03-20 05:24:29, Matthew Wilcox wrote:

From: "Matthew Wilcox (Oracle)" <willy@infradead.org>

By moving PG_writeback down into the low bits of the page flags, we can
use clear_bit_unlock_is_negative_byte() for writeback as well as the
lock bit.  wake_up_page() then has no more callers.  Given the other
code being executed between the clear and the test, this is not going
to be as dramatic a win as it was for PageLocked, but symmetry between
the two is nice and lets us remove some code.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>

The patch looks good to me. Just one nit:

+	VM_BUG_ON_PAGE(!PageWriteback(page), page);
+	if (__clear_page_writeback(page))
+		wake_up_page_bit(page, PG_writeback);

Since __clear_page_writeback() isn't really prepared for PageWriteback()
not being set, can we move the VM_BUG_ON_PAGE() there? Otherwise feel free
to add:

Reviewed-by: Jan Kara <jack@suse.cz>

								Honza
-- 
Jan Kara [off-list ref]
SUSE Labs, CR