kernel/linux.git/mm/cma_debug.c, branch v6.19.11

mm: cma: simplify cma_maxchunk_get()

2025-07-25T02:12:36+00:00

The function opencodes for_each_clear_bitrange(). Fix that and drop most of housekeeping code. Link: https://lkml.kernel.org/r/20250719205401.399475-3-yury.norov@gmail.com Signed-off-by: Yury Norov (NVIDIA) Acked-by: David Hildenbrand Signed-off-by: Andrew Morton

mm, cma: support multiple contiguous ranges, if requested

2025-03-17T05:06:25+00:00

Currently, CMA manages one range of physically contiguous memory. Creation of larger CMA areas with hugetlb_cma may run in to gaps in physical memory, so that they are not able to allocate that contiguous physical range from memblock when creating the CMA area. This can happen, for example, on an AMD system with > 1TB of memory, where there will be a gap just below the 1TB (40bit DMA) line. If you have set aside most of memory for potential hugetlb CMA allocation, cma_declare_contiguous_nid will fail. hugetlb_cma doesn't need the entire area to be one physically contiguous range. It just cares about being able to get physically contiguous chunks of a certain size (e.g. 1G), and it is fine to have the CMA area backed by multiple physical ranges, as long as it gets 1G contiguous allocations. Multi-range support is implemented by introducing an array of ranges, instead of just one big one. Each range has its own bitmap. Effectively, the allocate and release operations work as before, just per-range. So, instead of going through one large bitmap, they now go through a number of smaller ones. The maximum number of supported ranges is 8, as defined in CMA_MAX_RANGES. Since some current users of CMA expect a CMA area to just use one physically contiguous range, only allow for multiple ranges if a new interface, cma_declare_contiguous_nid_multi, is used. The other interfaces will work like before, creating only CMA areas with 1 range. cma_declare_contiguous_nid_multi works as follows, mimicking the default "bottom-up, above 4G" reservation approach: 0) Try cma_declare_contiguous_nid, which will use only one region. If this succeeds, return. This makes sure that for all the cases that currently work, the behavior remains unchanged even if the caller switches from cma_declare_contiguous_nid to cma_declare_contiguous_nid_multi. 1) Select the largest free memblock ranges above 4G, with a maximum number of CMA_MAX_RANGES. 2) If we did not find at most CMA_MAX_RANGES that add up to the total size requested, return -ENOMEM. 3) Sort the selected ranges by base address. 4) Reserve them bottom-up until we get what we wanted. Link: https://lkml.kernel.org/r/20250228182928.2645936-3-fvdl@google.com Signed-off-by: Frank van der Linden Cc: Arnd Bergmann Cc: Alexander Gordeev Cc: Andy Lutomirski Cc: Dan Carpenter Cc: Dave Hansen Cc: David Hildenbrand Cc: Heiko Carstens Cc: Joao Martins Cc: Johannes Weiner Cc: Madhavan Srinivasan Cc: Michael Ellerman Cc: Muchun Song Cc: Oscar Salvador Cc: Peter Zijlstra Cc: Roman Gushchin (Cruise) Cc: Usama Arif Cc: Vasily Gorbik Cc: Yu Zhao Cc: Zi Yan Signed-off-by: Andrew Morton

mm/cma: export total and free number of pages for CMA areas

2025-03-17T05:06:24+00:00

Patch series "hugetlb/CMA improvements for large systems", v5. On large systems, we observed some issues with hugetlb and CMA: 1) When specifying a large number of hugetlb boot pages (hugepages= on the commandline), the kernel may run out of memory before it even gets to HVO. For example, if you have a 3072G system, and want to use 3024 1G hugetlb pages for VMs, that should leave you plenty of space for the hypervisor, provided you have the hugetlb vmemmap optimization (HVO) enabled. However, since the vmemmap pages are always allocated first, and then later in boot freed, you will actually run yourself out of memory before you can do HVO. This means not getting all the hugetlb pages you want, and worse, failure to boot if there is an allocation failure in the system from which it can't recover. 2) There is a system setup where you might want to use hugetlb_cma with a large value (say, again, 3024 out of 3072G like above), and then lower that if system usage allows it, to make room for non-hugetlb processes. For this, a variation of the problem above applies: the kernel runs out of unmovable space to allocate from before you finish boot, since your CMA area takes up all the space. 3) CMA wants to use one big contiguous area for allocations. Which fails if you have the aforementioned 3T system with a gap in the middle of physical memory (like the < 40bits BIOS DMA area seen on some AMD systems). You then won't be able to set up a CMA area for one of the NUMA nodes, leading to loss of half of your hugetlb CMA area. 4) Under the scenario mentioned in 2), when trying to grow the number of hugetlb pages after dropping it for a while, new CMA allocations may fail occasionally. This is not unexpected, some transient references on pages may prevent cma_alloc from succeeding under memory pressure. However, the hugetlb code then falls back to a normal contiguous alloc, which may end up succeeding. This is not always desired behavior. If you have a large CMA area, then the kernel has a restricted amount of memory it can do unmovable allocations from (a well known issue). A normal contiguous alloc may eat further in to this space. To resolve these issues, do the following: * Add hooks to the section init code to do custom initialization of memmap pages. Hugetlb bootmem (memblock) allocated pages can then be pre-HVOed. This avoids allocating a large number of vmemmap pages early in boot, only to have them be freed again later, and also avoids running out of memory as described under 1). Using these hooks for hugetlb is optional. It requires moving hugetlb bootmem allocation to an earlier spot by the architecture. This has been enabled on x86. * hugetlb_cma doesn't care about the CMA area it uses being one large contiguous range. Multiple smaller ranges are fine. The only requirements are that the areas should be on one NUMA node, and individual gigantic pages should be allocatable from them. So, implement multi-range support for CMA, avoiding issue 3). * Introduce a hugetlb_cma_only option on the commandline. This only allows allocations from CMA for gigantic pages, if hugetlb_cma= is also specified. * With hugetlb_cma_only active, it also makes sense to be able to pre-allocate gigantic hugetlb pages at boot time from the CMA area(s). Add a rudimentary early CMA allocation interface, that just grabs a piece of memblock-allocated space from the CMA area, which gets marked as allocated in the CMA bitmap when the CMA area is initialized. With this, hugepages= can be supported with hugetlb_cma=, making scenario 2) work. Additionally, fix some minor bugs, with one worth mentioning: since hugetlb gigantic bootmem pages are allocated by memblock, they may span multiple zones, as memblock doesn't (and mostly can't) know about zones. This can cause problems. A hugetlb page spanning multiple zones is bad, and it's worse with HVO, when the de-HVO step effectively sneakily re-assigns pages to a different zone than originally configured, since the tail pages all inherit the zone from the first 60 tail pages. This condition is not common, but can be easily reproduced using ZONE_MOVABLE. To fix this, add checks to see if gigantic bootmem pages intersect with multiple zones, and do not use them if they do, giving them back to the page allocator instead. The first patch is kind of along for the ride, except that maintaining an available_count for a CMA area is convenient for the multiple range support. This patch (of 27): In addition to the number of allocations and releases, system management software may like to be aware of the size of CMA areas, and how many pages are available in it. This information is currently not available, so export it in total_page and available_pages, respectively. The name 'available_pages' was picked over 'free_pages' because 'free' implies that the pages are unused. But they might not be, they just haven't been used by cma_alloc The number of available pages is tracked regardless of CONFIG_CMA_SYSFS, allowing for a few minor shortcuts in the code, avoiding bitmap operations. Link: https://lkml.kernel.org/r/20250228182928.2645936-2-fvdl@google.com Signed-off-by: Frank van der Linden Reviewed-by: Oscar Salvador Cc: David Hildenbrand Cc: Joao Martins Cc: Muchun Song Cc: Roman Gushchin (Cruise) Cc: Usama Arif Cc: Yu Zhao Cc: Zi Yan Cc: Alexander Gordeev Cc: Andy Lutomirski Cc: Arnd Bergmann Cc: Dan Carpenter Cc: Dave Hansen Cc: Heiko Carstens Cc: Johannes Weiner Cc: Madhavan Srinivasan Cc: Michael Ellerman Cc: Peter Zijlstra Cc: Vasily Gorbik Signed-off-by: Andrew Morton

mm/cma_debug: show complete cma name in debugfs directories

2022-09-12T03:25:50+00:00

Currently only 12 characters of the cma name is being used as the debug directories where as the cma name can be of length CMA_MAX_NAME(=64) characters. One side problem with this is having 2 cma's with first common 12 characters would end up in trying to create directories with same name and fails with -EEXIST thus can limit cma debug functionality. The 'cma-' prefix is used initially where cma areas don't have any names and are represented by simple integer values. Since now each cma would be having its own name, drop 'cma-' prefix for the cma debug directories as they are clearly evident that they are for cma debug through creating them in /sys/kernel/debug/cma/ path. Link: https://lkml.kernel.org/r/1660223729-22461-1-git-send-email-quic_charante@quicinc.com Signed-off-by: Charan Teja Kalla Cc: David Hildenbrand Cc: Vlastimil Babka Cc: Pavan Kondeti Cc: Minchan Kim Signed-off-by: Andrew Morton

mm/cma_debug.c: align the name buffer length as struct cma

2022-07-30T01:07:16+00:00

Avoids truncating the debugfs output to 16 chars. Potentially alters the userspace output, but this is a debugfs interface and there are no stability guarantees. Link: https://lkml.kernel.org/r/20220719091554.27864-1-quic_yingangl@quicinc.com Signed-off-by: Kassey Li Cc: Sasha Levin Cc: Joonsoo Kim Cc: Minchan Kim Signed-off-by: Andrew Morton

mm/cma: change cma mutex to irq safe spinlock

2021-05-05T18:27:21+00:00

Patch series "make hugetlb put_page safe for all calling contexts", v5. This effort is the result a recent bug report [1]. Syzbot found a potential deadlock in the hugetlb put_page/free_huge_page_path. WARNING: SOFTIRQ-safe -> SOFTIRQ-unsafe lock order detected Since the free_huge_page_path already has code to 'hand off' page free requests to a workqueue, a suggestion was proposed to make the in_irq() detection accurate by always enabling PREEMPT_COUNT [2]. The outcome of that discussion was that the hugetlb put_page path (free_huge_page) path should be properly fixed and safe for all calling contexts. [1] https://lore.kernel.org/linux-mm/000000000000f1c03b05bc43aadc@google.com/ [2] http://lkml.kernel.org/r/20210311021321.127500-1-mike.kravetz@oracle.com This patch (of 8): cma_release is currently a sleepable operatation because the bitmap manipulation is protected by cma->lock mutex. Hugetlb code which relies on cma_release for CMA backed (giga) hugetlb pages, however, needs to be irq safe. The lock doesn't protect any sleepable operation so it can be changed to a (irq aware) spin lock. The bitmap processing should be quite fast in typical case but if cma sizes grow to TB then we will likely need to replace the lock by a more optimized bitmap implementation. Link: https://lkml.kernel.org/r/20210409205254.242291-1-mike.kravetz@oracle.com Link: https://lkml.kernel.org/r/20210409205254.242291-2-mike.kravetz@oracle.com Signed-off-by: Mike Kravetz Acked-by: Michal Hocko Reviewed-by: David Hildenbrand Acked-by: Roman Gushchin Cc: Shakeel Butt Cc: Oscar Salvador Cc: Muchun Song Cc: David Rientjes Cc: Miaohe Lin Cc: Peter Zijlstra Cc: Matthew Wilcox Cc: HORIGUCHI NAOYA Cc: "Aneesh Kumar K . V" Cc: Waiman Long Cc: Peter Xu Cc: Mina Almasry Cc: Hillf Danton Cc: Joonsoo Kim Cc: Barry Song Cc: Will Deacon Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

debugfs: make sure we can remove u32_array files cleanly

2020-07-10T20:54:00+00:00

debugfs_create_u32_array() allocates a small structure to wrap the data and size information about the array. If users ever try to remove the file this leads to a leak since nothing ever frees this wrapper. That said there are no upstream users of debugfs_create_u32_array() that'd remove a u32 array file (we only have one u32 array user in CMA), so there is no real bug here. Make callers pass a wrapper they allocated. This way the lifetime management of the wrapper is on the caller, and we can avoid the potential leak in debugfs. CC: Chucheng Luo Signed-off-by: Jakub Kicinski Reviewed-by: Greg Kroah-Hartman Signed-off-by: David S. Miller

mm/cma_debug.c: use DEFINE_DEBUGFS_ATTRIBUTE to define debugfs fops

2019-12-01T20:59:09+00:00

It is more clear to use DEFINE_DEBUGFS_ATTRIBUTE to define debugfs file operation rather than DEFINE_SIMPLE_ATTRIBUTE. Link: http://lkml.kernel.org/r/1572348687-9951-1-git-send-email-zhongjiang@huawei.com Signed-off-by: zhong jiang Reviewed-by: Andrew Morton Cc: Yue Hu Cc: Greg Kroah-Hartman Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm/cma_debug.c: fix the break condition in cma_maxchunk_get()

2019-05-14T16:47:45+00:00

If not find zero bit in find_next_zero_bit(), it will return the size parameter passed in, so the start bit should be compared with bitmap_maxno rather than cma->count. Although getting maxchunk is working fine due to zero value of order_per_bit currently, the operation will be stuck if order_per_bit is set as non-zero. Link: http://lkml.kernel.org/r/20190319092734.276-1-zbestahu@gmail.com Signed-off-by: Yue Hu Reviewed-by: Andrew Morton Cc: Michal Hocko Cc: Joe Perches Cc: David Rientjes Cc: Dmitry Safonov Cc: Joonsoo Kim Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm/cma_debug.c: remove static scoped cma_debugfs_root

2019-03-06T05:07:20+00:00

Currently cma_debugfs_root is static storage. That is unnecessary since it will be only used by next cma_debugfs_add_one(). We can just pass it to following calling to save thisspace. Also remove useless idx parameter. Link: http://lkml.kernel.org/r/20190221040130.8940-1-zbestahu@gmail.com Signed-off-by: Yue Hu Reviewed-by: Andrew Morton Cc: Michal Hocko Cc: David Rientjes Cc: Joe Perches Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds