user/sven/linux.git/include/linux/mmzone.h, branch v4.4.2

include/linux/mmzone.h: reflow comment

2015-11-07T01:50:42Z

Someone has an 86 column display. Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm, page_alloc: reserve pageblocks for high-order atomic allocations on demand

2015-11-07T01:50:42Z

High-order watermark checking exists for two reasons -- kswapd high-order awareness and protection for high-order atomic requests. Historically the kernel depended on MIGRATE_RESERVE to preserve min_free_kbytes as high-order free pages for as long as possible. This patch introduces MIGRATE_HIGHATOMIC that reserves pageblocks for high-order atomic allocations on demand and avoids using those blocks for order-0 allocations. This is more flexible and reliable than MIGRATE_RESERVE was. A MIGRATE_HIGHORDER pageblock is created when an atomic high-order allocation request steals a pageblock but limits the total number to 1% of the zone. Callers that speculatively abuse atomic allocations for long-lived high-order allocations to access the reserve will quickly fail. Note that SLUB is currently not such an abuser as it reclaims at least once. It is possible that the pageblock stolen has few suitable high-order pages and will need to steal again in the near future but there would need to be strong justification to search all pageblocks for an ideal candidate. The pageblocks are unreserved if an allocation fails after a direct reclaim attempt. The watermark checks account for the reserved pageblocks when the allocation request is not a high-order atomic allocation. The reserved pageblocks can not be used for order-0 allocations. This may allow temporary wastage until a failed reclaim reassigns the pageblock. This is deliberate as the intent of the reservation is to satisfy a limited number of atomic high-order short-lived requests if the system requires them. The stutter benchmark was used to evaluate this but while it was running there was a systemtap script that randomly allocated between 1 high-order page and 12.5% of memory's worth of order-3 pages using GFP_ATOMIC. This is much larger than the potential reserve and it does not attempt to be realistic. It is intended to stress random high-order allocations from an unknown source, show that there is a reduction in failures without introducing an anomaly where atomic allocations are more reliable than regular allocations. The amount of memory reserved varied throughout the workload as reserves were created and reclaimed under memory pressure. The allocation failures once the workload warmed up were as follows; 4.2-rc5-vanilla 70% 4.2-rc5-atomic-reserve 56% The failure rate was also measured while building multiple kernels. The failure rate was 14% but is 6% with this patch applied. Overall, this is a small reduction but the reserves are small relative to the number of allocation requests. In early versions of the patch, the failure rate reduced by a much larger amount but that required much larger reserves and perversely made atomic allocations seem more reliable than regular allocations. [yalin.wang2010@gmail.com: fix redundant check and a memory leak] Signed-off-by: Mel Gorman Acked-by: Vlastimil Babka Acked-by: Michal Hocko Acked-by: Johannes Weiner Cc: Christoph Lameter Cc: David Rientjes Cc: Vitaly Wool Cc: Rik van Riel Signed-off-by: yalin wang Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm, page_alloc: remove MIGRATE_RESERVE

2015-11-07T01:50:42Z

MIGRATE_RESERVE preserves an old property of the buddy allocator that existed prior to fragmentation avoidance -- min_free_kbytes worth of pages tended to remain contiguous until the only alternative was to fail the allocation. At the time it was discovered that high-order atomic allocations relied on this property so MIGRATE_RESERVE was introduced. A later patch will introduce an alternative MIGRATE_HIGHATOMIC so this patch deletes MIGRATE_RESERVE and supporting code so it'll be easier to review. Note that this patch in isolation may look like a false regression if someone was bisecting high-order atomic allocation failures. Signed-off-by: Mel Gorman Acked-by: Vlastimil Babka Cc: Christoph Lameter Cc: David Rientjes Cc: Johannes Weiner Cc: Michal Hocko Cc: Vitaly Wool Cc: Rik van Riel Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm, page_alloc: delete the zonelist_cache

2015-11-07T01:50:42Z

The zonelist cache (zlc) was introduced to skip over zones that were recently known to be full. This avoided expensive operations such as the cpuset checks, watermark calculations and zone_reclaim. The situation today is different and the complexity of zlc is harder to justify. 1) The cpuset checks are no-ops unless a cpuset is active and in general are a lot cheaper. 2) zone_reclaim is now disabled by default and I suspect that was a large source of the cost that zlc wanted to avoid. When it is enabled, it's known to be a major source of stalling when nodes fill up and it's unwise to hit every other user with the overhead. 3) Watermark checks are expensive to calculate for high-order allocation requests. Later patches in this series will reduce the cost of the watermark checking. 4) The most important issue is that in the current implementation it is possible for a failed THP allocation to mark a zone full for order-0 allocations and cause a fallback to remote nodes. The last issue could be addressed with additional complexity but as the benefit of zlc is questionable, it is better to remove it. If stalls due to zone_reclaim are ever reported then an alternative would be to introduce deferring logic based on a timeout inside zone_reclaim itself and leave the page allocator fast paths alone. The impact on page-allocator microbenchmarks is negligible as they don't hit the paths where the zlc comes into play. Most page-reclaim related workloads showed no noticeable difference as a result of the removal. The impact was noticeable in a workload called "stutter". One part uses a lot of anonymous memory, a second measures mmap latency and a third copies a large file. In an ideal world the latency application would not notice the mmap latency. On a 2-node machine the results of this patch are stutter 4.3.0-rc1 4.3.0-rc1 baseline nozlc-v4 Min mmap 20.9243 ( 0.00%) 20.7716 ( 0.73%) 1st-qrtle mmap 22.0612 ( 0.00%) 22.0680 ( -0.03%) 2nd-qrtle mmap 22.3291 ( 0.00%) 22.3809 ( -0.23%) 3rd-qrtle mmap 25.2244 ( 0.00%) 25.2396 ( -0.06%) Max-90% mmap 48.0995 ( 0.00%) 28.3713 ( 41.02%) Max-93% mmap 52.5557 ( 0.00%) 36.0170 ( 31.47%) Max-95% mmap 55.8173 ( 0.00%) 47.3163 ( 15.23%) Max-99% mmap 67.3781 ( 0.00%) 70.1140 ( -4.06%) Max mmap 24447.6375 ( 0.00%) 12915.1356 ( 47.17%) Mean mmap 33.7883 ( 0.00%) 27.7944 ( 17.74%) Best99%Mean mmap 27.7825 ( 0.00%) 25.2767 ( 9.02%) Best95%Mean mmap 26.3912 ( 0.00%) 23.7994 ( 9.82%) Best90%Mean mmap 24.9886 ( 0.00%) 23.2251 ( 7.06%) Best50%Mean mmap 22.0157 ( 0.00%) 22.0261 ( -0.05%) Best10%Mean mmap 21.6705 ( 0.00%) 21.6083 ( 0.29%) Best5%Mean mmap 21.5581 ( 0.00%) 21.4611 ( 0.45%) Best1%Mean mmap 21.3079 ( 0.00%) 21.1631 ( 0.68%) Note that the maximum stall latency went from 24 seconds to 12 which is still bad but an improvement. The milage varies considerably 2-node machine on an earlier test went from 494 seconds to 47 seconds and a 4-node machine that tested an earlier version of this patch went from a worst case stall time of 6 seconds to 67ms. The nature of the benchmark is inherently unpredictable as it is hammering the system and the milage will vary between machines. There is a secondary impact with potentially more direct reclaim because zones are now being considered instead of being skipped by zlc. In this particular test run it did not occur so will not be described. However, in at least one test the following was observed 1. Direct reclaim rates were higher. This was likely due to direct reclaim being entered instead of the zlc disabling a zone and busy looping. Busy looping may have the effect of allowing kswapd to make more progress and in some cases may be better overall. If this is found then the correct action is to put direct reclaimers to sleep on a waitqueue and allow kswapd make forward progress. Busy looping on the zlc is even worse than when the allocator used to blindly call congestion_wait(). 2. There was higher swap activity as direct reclaim was active. 3. Direct reclaim efficiency was lower. This is related to 1 as more scanning activity also encountered more pages that could not be immediately reclaimed In that case, the direct page scan and reclaim rates are noticeable but it is not considered a problem for a few reasons 1. The test is primarily concerned with latency. The mmap attempts are also faulted which means there are THP allocation requests. The ZLC could cause zones to be disabled causing the process to busy loop instead of reclaiming. This looks like elevated direct reclaim activity but it's the correct action to take based on what processes requested. 2. The test hammers reclaim and compaction heavily. The number of successful THP faults is highly variable but affects the reclaim stats. It's not a realistic or reasonable measure of page reclaim activity. 3. No other page-reclaim intensive workload that was tested showed a problem. 4. If a workload is identified that benefitted from the busy looping then it should be fixed by having direct reclaimers sleep on a wait queue until woken by kswapd instead of busy looping. We had this class of problem before when congestion_waits() with a fixed timeout was a brain damaged decision but happened to benefit some workloads. If a workload is identified that relied on the zlc to busy loop then it should be fixed correctly and have a direct reclaimer sleep on a waitqueue until woken by kswapd. Signed-off-by: Mel Gorman Acked-by: David Rientjes Acked-by: Christoph Lameter Acked-by: Vlastimil Babka Acked-by: Michal Hocko Acked-by: Johannes Weiner Cc: Vitaly Wool Cc: Rik van Riel Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm, page_alloc: use masks and shifts when converting GFP flags to migrate types

2015-11-07T01:50:42Z

This patch redefines which GFP bits are used for specifying mobility and the order of the migrate types. Once redefined it's possible to convert GFP flags to a migrate type with a simple mask and shift. The only downside is that readers of OOM kill messages and allocation failures may have been used to the existing values but scripts/gfp-translate will help. Signed-off-by: Mel Gorman Acked-by: Vlastimil Babka Cc: Christoph Lameter Cc: David Rientjes Cc: Johannes Weiner Cc: Michal Hocko Cc: Vitaly Wool Cc: Rik van Riel Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm, page_alloc: remove unnecessary parameter from zone_watermark_ok_safe

2015-11-07T01:50:42Z

Overall, the intent of this series is to remove the zonelist cache which was introduced to avoid high overhead in the page allocator. Once this is done, it is necessary to reduce the cost of watermark checks. The series starts with minor micro-optimisations. Next it notes that GFP flags that affect watermark checks are abused. __GFP_WAIT historically identified callers that could not sleep and could access reserves. This was later abused to identify callers that simply prefer to avoid sleeping and have other options. A patch distinguishes between atomic callers, high-priority callers and those that simply wish to avoid sleep. The zonelist cache has been around for a long time but it is of dubious merit with a lot of complexity and some issues that are explained. The most important issue is that a failed THP allocation can cause a zone to be treated as "full". This potentially causes unnecessary stalls, reclaim activity or remote fallbacks. The issues could be fixed but it's not worth it. The series places a small number of other micro-optimisations on top before examining GFP flags watermarks. High-order watermarks enforcement can cause high-order allocations to fail even though pages are free. The watermark checks both protect high-order atomic allocations and make kswapd aware of high-order pages but there is a much better way that can be handled using migrate types. This series uses page grouping by mobility to reserve pageblocks for high-order allocations with the size of the reservation depending on demand. kswapd awareness is maintained by examining the free lists. By patch 12 in this series, there are no high-order watermark checks while preserving the properties that motivated the introduction of the watermark checks. This patch (of 10): No user of zone_watermark_ok_safe() specifies alloc_flags. This patch removes the unnecessary parameter. Signed-off-by: Mel Gorman Acked-by: David Rientjes Acked-by: Vlastimil Babka Acked-by: Michal Hocko Reviewed-by: Christoph Lameter Acked-by: Johannes Weiner Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm/page_alloc: remove unused parameter in init_currently_empty_zone()

2015-11-06T03:34:48Z

Commit a2f3aa025766 ("[PATCH] Fix sparsemem on Cell") fixed an oops experienced on the Cell architecture when init-time functions, early_*(), are called at runtime by introducing an 'enum memmap_context' parameter to memmap_init_zone() and init_currently_empty_zone(). This parameter is intended to be used to tell whether the call of these two functions is being made on behalf of a hotplug event, or happening at boot-time. However, init_currently_empty_zone() does not use this parameter at all, so remove it. Signed-off-by: Yaowei Bai Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

Merge tag 'libnvdimm-for-4.3' of git://git.kernel.org/pub/scm/linux/kernel/git/nvdimm/nvdimm

2015-09-08T21:35:59Z

Pull libnvdimm updates from Dan Williams: "This update has successfully completed a 0day-kbuild run and has appeared in a linux-next release. The changes outside of the typical drivers/nvdimm/ and drivers/acpi/nfit.[ch] paths are related to the removal of IORESOURCE_CACHEABLE, the introduction of memremap(), and the introduction of ZONE_DEVICE + devm_memremap_pages(). Summary: - Introduce ZONE_DEVICE and devm_memremap_pages() as a generic mechanism for adding device-driver-discovered memory regions to the kernel's direct map. This facility is used by the pmem driver to enable pfn_to_page() operations on the page frames returned by DAX ('direct_access' in 'struct block_device_operations'). For now, the 'memmap' allocation for these "device" pages comes from "System RAM". Support for allocating the memmap from device memory will arrive in a later kernel. - Introduce memremap() to replace usages of ioremap_cache() and ioremap_wt(). memremap() drops the __iomem annotation for these mappings to memory that do not have i/o side effects. The replacement of ioremap_cache() with memremap() is limited to the pmem driver to ease merging the api change in v4.3. Completion of the conversion is targeted for v4.4. - Similar to the usage of memcpy_to_pmem() + wmb_pmem() in the pmem driver, update the VFS DAX implementation and PMEM api to provide persistence guarantees for kernel operations on a DAX mapping. - Convert the ACPI NFIT 'BLK' driver to map the block apertures as cacheable to improve performance. - Miscellaneous updates and fixes to libnvdimm including support for issuing "address range scrub" commands, clarifying the optimal 'sector size' of pmem devices, a clarification of the usage of the ACPI '_STA' (status) property for DIMM devices, and other minor fixes" * tag 'libnvdimm-for-4.3' of git://git.kernel.org/pub/scm/linux/kernel/git/nvdimm/nvdimm: (34 commits) libnvdimm, pmem: direct map legacy pmem by default libnvdimm, pmem: 'struct page' for pmem libnvdimm, pfn: 'struct page' provider infrastructure x86, pmem: clarify that ARCH_HAS_PMEM_API implies PMEM mapped WB add devm_memremap_pages mm: ZONE_DEVICE for "device memory" mm: move __phys_to_pfn and __pfn_to_phys to asm/generic/memory_model.h dax: drop size parameter to ->direct_access() nd_blk: change aperture mapping from WC to WB nvdimm: change to use generic kvfree() pmem, dax: have direct_access use __pmem annotation dax: update I/O path to do proper PMEM flushing pmem: add copy_from_iter_pmem() and clear_pmem() pmem, x86: clean up conditional pmem includes pmem: remove layer when calling arch_has_wmb_pmem() pmem, x86: move x86 PMEM API to new pmem.h header libnvdimm, e820: make CONFIG_X86_PMEM_LEGACY a tristate option pmem: switch to devm_ allocations devres: add devm_memremap libnvdimm, btt: write and validate parent_uuid ...

mm: remove struct node_active_region

2015-09-04T23:54:41Z

struct node_active_region is not used anymore. Remove it. Signed-off-by: minkyung88.kim Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm: ZONE_DEVICE for "device memory"

2015-08-27T23:40:58Z

While pmem is usable as a block device or via DAX mappings to userspace there are several usage scenarios that can not target pmem due to its lack of struct page coverage. In preparation for "hot plugging" pmem into the vmemmap add ZONE_DEVICE as a new zone to tag these pages separately from the ones that are subject to standard page allocations. Importantly "device memory" can be removed at will by userspace unbinding the driver of the device. Having a separate zone prevents allocation and otherwise marks these pages that are distinct from typical uniform memory. Device memory has different lifetime and performance characteristics than RAM. However, since we have run out of ZONES_SHIFT bits this functionality currently depends on sacrificing ZONE_DMA. Cc: H. Peter Anvin Cc: Ingo Molnar Cc: Dave Hansen Cc: Rik van Riel Cc: Mel Gorman Cc: Jerome Glisse [hch: various simplifications in the arch interface] Signed-off-by: Christoph Hellwig Signed-off-by: Dan Williams