kernel-ark/Documentation/vm
Hugh Dickins 5d337b9194 [PATCH] swap: swap_lock replace list+device
The idea of a swap_device_lock per device, and a swap_list_lock over them all,
is appealing; but in practice almost every holder of swap_device_lock must
already hold swap_list_lock, which defeats the purpose of the split.

The only exceptions have been swap_duplicate, valid_swaphandles and an
untrodden path in try_to_unuse (plus a few places added in this series).
valid_swaphandles doesn't show up high in profiles, but swap_duplicate does
demand attention.  However, with the hold time in get_swap_pages so much
reduced, I've not yet found a load and set of swap device priorities to show
even swap_duplicate benefitting from the split.  Certainly the split is mere
overhead in the common case of a single swap device.

So, replace swap_list_lock and swap_device_lock by spinlock_t swap_lock
(generally we seem to prefer an _ in the name, and not hide in a macro).

If someone can show a regression in swap_duplicate, then probably we should
add a hashlock for the swap_map entries alone (shorts being anatomic), so as
to help the case of the single swap device too.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-09-05 00:05:42 -07:00
..
balance Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
hugetlbpage.txt Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
locking [PATCH] swap: swap_lock replace list+device 2005-09-05 00:05:42 -07:00
numa Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
overcommit-accounting Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00