Peter Zijlstra wrote:
On Fri, 2007-04-06 at 23:15 +1000, Nick Piggin wrote:
or given a key:
- lookup the page from key.shared.inode->i_mapping by key.shared.pgoff
possibly loading the page using mapping->a_ops->readpage().
For shared futexes, wouldn't i_mapping be worse, because you'd be
ping-ponging the tree_lock between processes, rather than have each
use their own mmap_sem?
Your lockless pagecache work would solve most of that, no?
Yeah it would.
That also only helps for the wakeup case too, doesn't it? You have
to use the vmas to find out which inode to use to do the wait, I think?
(unless you introduce a new shared futex API).
one could do something like this:
struct address_space *mapping = page_mapping(page);
if (!mapping || mapping == &swapper_space)
do_private_futex();
else
do_shared_futex(mapping->host, page->index, addr % PAGE_SIZE);
But alas, it seems I overlooked that the mmap_sem also protects the page
tables as pointed out by Hugh, so this is all in fain it seems.
A well.
Well if it turned out to be a real problem, we _could_ introduce a new
futex API that takes a file descriptor+offset.
The old futex API is basically just a shorthand for choosing between
shared and private, depending on what the vma at the given address
happens to be.
--
SUSE Labs, Novell Inc.
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