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2005-09-05[PATCH] swap: swap_lock replace list+deviceHugh Dickins
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[PATCH] swap: scan_swap_map latency breaksHugh Dickins
The get_swap_page/scan_swap_map latency can be so bad that even those without preemption configured deserve relief: periodically cond_resched. 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[PATCH] swap: scan_swap_map drop swap_device_lockHugh Dickins
get_swap_page has often shown up on latency traces, doing lengthy scans while holding two spinlocks. swap_list_lock is already dropped, now scan_swap_map drop swap_device_lock before scanning the swap_map. While scanning for an empty cluster, don't worry that racing tasks may allocate what was free and free what was allocated; but when allocating an entry, check it's still free after retaking the lock. Avoid dropping the lock in the expected common path. No barriers beyond the locks, just let the cookie crumble; highest_bit limit is volatile, but benign. Guard against swapoff: must check SWP_WRITEOK before allocating, must raise SWP_SCANNING reference count while in scan_swap_map, swapoff wait for that to fall - just use schedule_timeout, we don't want to burden scan_swap_map itself, and it's very unlikely that anyone can really still be in scan_swap_map once swapoff gets this far. 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[PATCH] swap: scan_swap_map restyledHugh Dickins
Rewrite scan_swap_map to allocate in just the same way as before (taking the next free entry SWAPFILE_CLUSTER-1 times, then restarting at the lowest wholly empty cluster, falling back to lowest entry if none), but with a view towards dropping the lock in the next patch. 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[PATCH] swap: get_swap_page drop swap_list_lockHugh Dickins
Rewrite get_swap_page to allocate in just the same sequence as before, but without holding swap_list_lock across its scan_swap_map. Decrement nr_swap_pages and update swap_list.next in advance, while still holding swap_list_lock. Skip full devices by testing highest_bit. Swapoff hold swap_device_lock as well as swap_list_lock to clear SWP_WRITEOK. Reduces lock contention when there are parallel swap devices of the same priority. 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[PATCH] swap: freeing update swap_list.nextHugh Dickins
This makes negligible difference in practice: but swap_list.next should not be updated to a higher prio in the general helper swap_info_get, but rather in swap_entry_free; and then only in the case when entry is actually freed. 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[PATCH] swap: swap unsigned int consistencyHugh Dickins
The swap header's unsigned int last_page determines the range of swap pages, but swap_info has been using int or unsigned long in some cases: use unsigned int throughout (except, in several places a local unsigned long is useful to avoid overflows when adding). Signed-off-by: Hugh Dickins <hugh@veritas.com> Signed-off-by: Jens Axboe <axboe@suse.de> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-09-05[PATCH] swap: show span of swap extentsHugh Dickins
The "Adding %dk swap" message shows the number of swap extents, as a guide to how fragmented the swapfile may be. But a useful further guide is what total extent they span across (sometimes scarily large). And there's no need to keep nr_extents in swap_info: it's unused after the initial message, so save a little space by keeping it on stack. 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[PATCH] swap: swap extent list is orderedHugh Dickins
There are several comments that swap's extent_list.prev points to the lowest extent: that's not so, it's extent_list.next which points to it, as you'd expect. And a couple of loops in add_swap_extent which go all the way through the list, when they should just add to the other end. Fix those up, and let map_swap_page search the list forwards: profiles shows it to be twice as quick that way - because prefetch works better on how the structs are typically kmalloc'ed? or because usually more is written to than read from swap, and swap is allocated ascendingly? 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[PATCH] swap: move destroy_swap_extents callsHugh Dickins
sys_swapon's call to destroy_swap_extents on failure is made after the final swap_list_unlock, which is faintly unsafe: another sys_swapon might already be setting up that swap_info_struct. Calling it earlier, before taking swap_list_lock, is safe. sys_swapoff's call to destroy_swap_extents was safe, but likewise move it earlier, before taking the locks (once try_to_unuse has completed, nothing can be needing the swap extents). 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[PATCH] swap: correct swapfile nr_good_pagesHugh Dickins
If a regular swapfile lies on a filesystem whose blocksize is less than PAGE_SIZE, then setup_swap_extents may have to cut the number of usable swap pages; but sys_swapon's nr_good_pages was not expecting that. Also, setup_swap_extents takes no account of badpages listed in the swap header: not worth doing so, but ensure nr_badpages is 0 for a regular swapfile. 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[PATCH] swap: update swapfile i_sem commentHugh Dickins
Update swap extents comment: nowadays we guard with S_SWAPFILE not i_sem. Signed-off-by: Hugh Dickins <hugh@veritas.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-06-21[PATCH] can_share_swap_page: use page_mapcountHugh Dickins
Remember that ironic get_user_pages race? when the raised page_count on a page swapped out led do_wp_page to decide that it had to copy on write, so substituted a different page into userspace. 2.6.7 onwards have Andrea's solution, where try_to_unmap_one backs out if it finds page_count raised. Which works, but is unsatisfying (rmap.c has no other page_count heuristics), and was found a few months ago to hang an intensive page migration test. A year ago I was hesitant to engage page_mapcount, now it seems the right fix. So remove the page_count hack from try_to_unmap_one; and use activate_page in unuse_mm when dropping lock, to replace its secondary effect of helping swapoff to make progress in that case. Simplify can_share_swap_page (now called only on anonymous pages) to check page_mapcount + page_swapcount == 1: still needs the page lock to stabilize their (pessimistic) sum, but does not need swapper_space.tree_lock for that. In do_swap_page, move swap_free and unlock_page below page_add_anon_rmap, to keep sum on the high side, and correct when can_share_swap_page called. Signed-off-by: Hugh Dickins <hugh@veritas.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-05-17[PATCH] swapout oops fixMcMullan, Jason
Fix OOPS when swapping on a device that doesn't have an unplug_io_fn defined (eg, ATA Over Ethernet) Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-04-16Linux-2.6.12-rc2v2.6.12-rc2Linus Torvalds
Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!