On Wed, 25 Aug 2010, 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. > While I'd really love for callers to be able to gracefully handle getting a NULL back from the page allocator in all cases, it's not a prerequisite for this patchset. This patchset actually does nothing interesting except removing the __GFP_NOFAIL bit from their gfp mask. All of these allocations already loop looking for memory because they have orders that are less than PAGE_ALLOC_COSTLY_ORDER (which defaults to 3). So the loops in kzalloc_nofail(), etc., never actually loop. Demanding that the page allocator return order-3 memory in any context is a non-starter, so I'm not really interested in that. I'm more concerned about proper error handling being implemented for these callers iff someone redefines PAGE_ALLOC_COSTLY_ORDER to something else, perhaps even 0. Callers can, when desperate for memory, use GFP_ATOMIC to use some memory reserves across zones, hopefully order-0 and not an egregious amount. But the remainder of the burden really is back on the caller when this is depleted or it needs higher order allocs to be fixed in a way that doesn't rely on memory that doesn't exist. That's an implementation choice by the caller and I agree that some failsafe behavior is the only way that we don't get really bad results like corrupted user data or filesystems. -- 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
