Suspicious error for CMA stress test
From: guohanjun@huawei.com (Hanjun Guo)
Date: 2016-03-03 12:49:57
Also in:
linux-mm, lkml
On 2016/3/3 15:42, Joonsoo Kim wrote:
2016-03-03 10:25 GMT+09:00 Laura Abbott [off-list ref]:quoted
(cc -mm and Joonsoo Kim) On 03/02/2016 05:52 AM, Hanjun Guo wrote:quoted
Hi, I came across a suspicious error for CMA stress test: Before the test, I got: -bash-4.3# cat /proc/meminfo | grep Cma CmaTotal: 204800 kB CmaFree: 195044 kB After running the test: -bash-4.3# cat /proc/meminfo | grep Cma CmaTotal: 204800 kB CmaFree: 6602584 kB So the freed CMA memory is more than total.. Also the the MemFree is more than mem total: -bash-4.3# cat /proc/meminfo MemTotal: 16342016 kB MemFree: 22367268 kB MemAvailable: 22370528 kB
[...]
quoted
I played with this a bit and can see the same problem. The sanity check of CmaFree < CmaTotal generally triggers in __move_zone_freepage_state in unset_migratetype_isolate. This also seems to be present as far back as v4.0 which was the first version to have the updated accounting from Joonsoo. Were there known limitations with the new freepage accounting, Joonsoo?I don't know. I also played with this and looks like there is accounting problem, however, for my case, number of free page is slightly less than total. I will take a look. Hanjun, could you tell me your malloc_size? I tested with 1 and it doesn't look like your case.
I tested with malloc_size with 2M, and it grows much bigger than 1M, also I did some other test: - run with single thread with 100000 times, everything is fine. - I hack the cam_alloc() and free as below [1] to see if it's lock issue, with the same test with 100 multi-thread, then I got: -bash-4.3# cat /proc/meminfo | grep Cma CmaTotal: 204800 kB CmaFree: 225112 kB It only increased about 30M for free, not 6G+ in previous test, although the problem is not solved, the problem is less serious, is it a synchronization problem? Thanks Hanjun [1]: index ea506eb..4447494 100644
--- a/mm/cma.c
+++ b/mm/cma.c@@ -379,6 +379,7 @@ struct page *cma_alloc(struct cma *cma, size_t count, unsigned int align) if (!count) return NULL; + mutex_lock(&cma_mutex); mask = cma_bitmap_aligned_mask(cma, align); offset = cma_bitmap_aligned_offset(cma, align); bitmap_maxno = cma_bitmap_maxno(cma);
@@ -402,17 +403,16 @@ struct page *cma_alloc(struct cma *cma, size_t count, unsigned int align) mutex_unlock(&cma->lock); pfn = cma->base_pfn + (bitmap_no << cma->order_per_bit); - mutex_lock(&cma_mutex); ret = alloc_contig_range(pfn, pfn + count, MIGRATE_CMA); - mutex_unlock(&cma_mutex); if (ret == 0) { page = pfn_to_page(pfn); break; } cma_clear_bitmap(cma, pfn, count); - if (ret != -EBUSY) + if (ret != -EBUSY) { break; + } pr_debug("%s(): memory range at %p is busy, retrying\n", __func__, pfn_to_page(pfn));
@@ -420,6 +420,7 @@ struct page *cma_alloc(struct cma *cma, size_t count, unsigned int align) start = bitmap_no + mask + 1; } + mutex_unlock(&cma_mutex); trace_cma_alloc(pfn, page, count, align); pr_debug("%s(): returned %p\n", __func__, page);
@@ -445,15 +446,19 @@ bool cma_release(struct cma *cma, const struct page *pages, unsigned int count) pr_debug("%s(page %p)\n", __func__, (void *)pages); + mutex_lock(&cma_mutex); pfn = page_to_pfn(pages); - if (pfn < cma->base_pfn || pfn >= cma->base_pfn + cma->count) + if (pfn < cma->base_pfn || pfn >= cma->base_pfn + cma->count) { + mutex_unlock(&cma_mutex); return false; + } VM_BUG_ON(pfn + count > cma->base_pfn + cma->count); free_contig_range(pfn, count); cma_clear_bitmap(cma, pfn, count); + mutex_unlock(&cma_mutex); trace_cma_release(pfn, pages, count); return true;