On Tue, 2007-06-19 at 14:37 -0700, Keshavamurthy, Anil S wrote: > plain text document attachment (intel_iommu_pf_memalloc.patch) > Intel IOMMU driver needs memory during DMA map calls to setup its internal > page tables and for other data structures. As we all know that these DMA > map calls are mostly called in the interrupt context or with the spinlock > held by the upper level drivers(network/storage drivers), so in order to > avoid any memory allocation failure due to low memory issues, > this patch makes memory allocation by temporarily setting PF_MEMALLOC > flags for the current task before making memory allocation calls. > > We evaluated mempools as a backup when kmem_cache_alloc() fails > and found that mempools are really not useful here because > 1) We don;t know for sure how much to reserve in advance
So you just unleashed an unbounded allocation context on PF_MEMALLOC? seems like a really really bad idea. > 2) And mempools are not useful for GFP_ATOMIC case (as we call > memory alloc functions with GFP_ATOMIC) Mempools work as intended with GFP_ATOMIC, it gets filled up to the specified number of elements using GFP_KERNEL (at creation time). This gives GFP_ATOMIC allocations nr_elements extra items once it would start failing. > With PF_MEMALLOC flag set in the current->flags, the VM subsystem avoids > any watermark checks before allocating memory thus guarantee'ing the > memory till the last free page. PF_MEMALLOC as is, is meant to salvage the VM from the typical VM deadlock. Using it as you do now is not something a driver should ever do, and I'm afraid I will have to strongly oppose this patch. You really really want to calculate an upper bound on your memory consumption and reserve this. So, I'm afraid I'll have to.. NACK! - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
