Hi, here's a late topic for discussion that came out of my patchset [1]. It would likely have to involve all three groups, as FS/IO people would benefit, but it's MM area. Background: The recent thread [2] inspired me to look into guaranteeing alignment for kmalloc() for power-of-two sizes. IIUC some usecases (see [2]) don't know the required sizes in advance in order to create named caches via kmem_cache_create() with explicit alignment parameter (which is the only way to guarantee alignment right now). Moreover, in most cases the alignment happens naturally as the slab allocators split power-of-two-sized pages into smaller power-of-two-sized objects. kmalloc() users then might rely on the alignment even unknowingly, until it breaks when e.g. SLUB debugging is enabled. Turns out it's not difficult to add the guarantees [1] and in the production SLAB/SLUB configurations nothing really changes as explained above. Then folks wouldn't have to come up with workarounds as in [2]. Technical downsides would be for SLUB debug mode (increased memory fragmentation, should be acceptable in a bug hunting scenario?), and SLOB (potentially worse performance due to increased packing effort, but this slab variant is rather marginal). In the session I hope to resolve the question whether this is indeed the right thing to do for all kmalloc() users, without an explicit alignment requests, and if it's worth the potentially worse performance/fragmentation it would impose on a hypothetical new slab implementation for which it wouldn't be optimal to split power-of-two sized pages into power-of-two-sized objects (or whether there are any other downsides). Thanks, Vlastimil [1] https://lore.kernel.org/lkml/20190319211108.15495-1-vbabka@xxxxxxx/T/#u [2] https://lore.kernel.org/linux-fsdevel/20190225040904.5557-1-ming.lei@xxxxxxxxxx/T/#u
