On Wed, Jan 17, 2024 at 09:12:26AM +1100, Dave Chinner wrote: > On Fri, Jan 12, 2024 at 01:18:27PM +0100, Uladzislau Rezki wrote: > > On Fri, Jan 12, 2024 at 07:37:36AM +1100, Dave Chinner wrote: > > > On Thu, Jan 11, 2024 at 04:54:48PM +0100, Uladzislau Rezki wrote: > > > > On Thu, Jan 11, 2024 at 08:02:16PM +1100, Dave Chinner wrote: > > > > > On Tue, Jan 02, 2024 at 07:46:29PM +0100, Uladzislau Rezki (Sony) wrote: > > > > > > Concurrent access to a global vmap space is a bottle-neck. > > > > > > We can simulate a high contention by running a vmalloc test > > > > > > suite. > > > > > > > > > > > > To address it, introduce an effective vmap node logic. Each > > > > > > node behaves as independent entity. When a node is accessed > > > > > > it serves a request directly(if possible) from its pool. > > > > > > > > > > > > This model has a size based pool for requests, i.e. pools are > > > > > > serialized and populated based on object size and real demand. > > > > > > A maximum object size that pool can handle is set to 256 pages. > > > > > > > > > > > > This technique reduces a pressure on the global vmap lock. > > > > > > > > > > > > Signed-off-by: Uladzislau Rezki (Sony) <urezki@xxxxxxxxx> > > > > > > > > > > Why not use a llist for this? That gets rid of the need for a > > > > > new pool_lock altogether... > > > > > > > > > Initially i used the llist. I have changed it because i keep track > > > > of objects per a pool to decay it later. I do not find these locks > > > > as contented one therefore i did not think much. > > > > > > Ok. I've used llist and an atomic counter to track the list length > > > in the past. > > > > > > But is the list length even necessary? It seems to me that it is > > > only used by the shrinker to determine how many objects are on the > > > lists for scanning, and I'm not sure that's entirely necessary given > > > the way the current global shrinker works (i.e. completely unfair to > > > low numbered nodes due to scan loop start bias). > > > > > I use the length to decay pools by certain percentage, currently it is > > 25%, so i need to know number of objects. It is done in the purge path. > > As for shrinker, once it hits us we drain pools entirely. > > Why does purge need to be different to shrinking? > > But, regardless, you can still use llist with an atomic counter to > do this - there is no need for a spin lock at all. > As i pointed earlier, i will have a look at it. > > > > Anyway, i will have a look at this to see if llist is easy to go with > > > > or not. If so i will send out a separate patch. > > > > > > Sounds good, it was just something that crossed my mind given the > > > pattern of "producer adds single items, consumer detaches entire > > > list, processes it and reattaches remainder" is a perfect match for > > > the llist structure. > > > > > The llist_del_first() has to be serialized. For this purpose a per-cpu > > pool would work or kind of "in_use" atomic that protects concurrent > > removing. > > So don't use llist_del_first(). > > > If we detach entire llist, then we need to keep track of last node > > to add it later as a "batch" to already existing/populated list. > > Why? I haven't see any need for ordering these lists which would > requiring strict tail-add ordered semantics. > I mean the following: 1. first = llist_del_all(&example); 2. last = llist_reverse_order(first); 4. va = __llist_del_first(first); /* * "example" might not be empty, use the batch. Otherwise * we loose the entries "example" pointed to. */ 3. llist_add_batch(first, last, &example); -- Uladzislau Rezki
