Hi everyone, The percpu memory using the valloc area based chunk allocator lazily populates chunks by first requesting the full virtual address space required for the chunk and subsequently adding pages as allocations come through. To ensure atomic allocations can succeed, a workqueue item is used to maintain a minimum number of empty pages. In certain scenarios, such as reported in [1], it is possible that physical memory becomes quite scarce which can result in either a rather long time spent trying to find free pages or worse, a kernel panic. This patchset introduces no retry semantics to percpu memory by allowing users to pass through certain flags controlled by a whitelist. In this case, only __GFP_NORETRY and __GFP_NOWARN are initially allowed. This should prevent the eventual kernel panic due to the workqueue item and now give flexibility to users to decide how they want to fail when the percpu allocator fails if they use the additional flags. This does not prevent the allocator from panicking should an allocation without the additional flags cause an underlying allocator to trigger out of memory. I tested this by running basic allocations with and without passing the additional flags. Allocations are able to proceed / fail as expected without triggering the out of memory kernel panic. I still saw OOM killer activate, but I attribute that to other programs faulting in the background. Without the flags, the kernel panics pretty quickly with the expected out of memory panic. [1] https://lkml.org/lkml/2018/2/12/551 This patchset contains the following 3 patches: 0001-percpu-match-chunk-allocator-declarations-with-defin.patch 0002-percpu-add-__GFP_NORETRY-semantics-to-the-percpu-bal.patch 0003-percpu-allow-select-gfp-to-be-passed-to-underlying-a.patch 0001 fixes out of sync declaration and definiton variable names. 0002 adds no retry semantics to the workqueue balance path. 0003 enables users to pass through flags to the underlying percpu memory allocators. This also cleans up the semantics surrounding how the flags are managed. This patchset is ontop of percpu#master 7928b2cbe5. diffstats below: Dennis Zhou (3): percpu: match chunk allocator declarations with definitions percpu: add __GFP_NORETRY semantics to the percpu balancing path percpu: allow select gfp to be passed to underlying allocators mm/percpu-km.c | 8 ++++---- mm/percpu-vm.c | 18 +++++++++++------- mm/percpu.c | 52 ++++++++++++++++++++++++++++++++++------------------ 3 files changed, 49 insertions(+), 29 deletions(-) Thanks, Dennis -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
