On Wed, Nov 18, 2009 at 05:56:46PM +0900, KOSAKI Motohiro wrote: > > On Tue, Nov 17, 2009 at 04:23:43PM +0900, KOSAKI Motohiro wrote: > > > > > > Non MM subsystem must not use PF_MEMALLOC. Memory reclaim need few > > > memory, anyone must not prevent it. Otherwise the system cause > > > mysterious hang-up and/or OOM Killer invokation. > > > > The xfsbufd is a woken run by a registered memory shaker. i.e. it > > runs when the system needs to reclaim memory. It forceѕ the > > delayed write metadata buffers (of which there can be a lot) to disk > > so that they can be reclaimed on IO completion. This IO submission > > may require ѕome memory to be allocated to be able to free that > > memory. > > > > Hence, AFAICT the use of PF_MEMALLOC is valid here. > > Thanks a lot. > I have one additional question, may I ask you? > > How can we calculate maximum memory usage in xfsbufd? It doesn't get calculated at the moment. It is very difficult to calculate a usable size metric for it because there are multiple caches (up to 3 per filesystem), and dentry/inode reclaim causes the size of the cache to grow. Hence the size of the cache is not really something that can be considered a stable or predictable input into a "reclaim now" calculation. As such we simply cause xfsbufd run simultaneously with the shrinkers that cause it to grow.... > I'm afraid that VM and XFS works properly but adding two makes memory exhaust. I don't understand what you are trying to say here. > And, I conclude XFS doesn't need sharing reservation memory with VM, > it only need non failed allocation. right? IOW I'm prefer perter's > suggestion. Right. However, it is worth keeping in mind that this is a performance critical path for inode reclaim. Hence any throttling of allocation will slow down the rate at which memory is freed by the system.... Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
