On Wed, Aug 25, 2010 at 03:35:42PM +0200, Peter Zijlstra wrote: > > While I appreciate that it might be somewhat (a lot) harder for a > filesystem to provide that guarantee, I'd be deeply worried about your > claim that its impossible. > > It would render a system without swap very prone to deadlocks. Even with > the very tight dirty page accounting we currently have you can fill all > your memory with anonymous pages, at which point there's nothing free > and you require writeout of dirty pages to succeed. For file systems that do delayed allocation, the situation is very similar to swapping over NFS. Sometimes in order to make some free memory, you need to spend some free memory... which implies that for these file systems, being more aggressive about triggering writeout, and being more aggressive about throttling processes which are creating too many dirty pages, especially dirty delayed allocaiton pages (regardless of whether this is via write(2) or accessing mmapped memory), is a really good idea. A pool of free pages which is reserved for routines that are doing page cleaning would probably also be a good idea. Maybe that's just retrying with GFP_ATOMIC if a normal allocation fails, or maybe we need our own special pool, or maybe we need to dynamically resize the GFP_ATOMIC pool based on how many subsystems might need to use it.... Just brainstorming here; what do people think? - Ted -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
