Hi, I have a failure of allocation of virtual memory on ARMv7 based platform. I called alloc_page()/vm_map_ram() for allocation/mapping pages. Virtual memory space exhausting problem occurred. I checked virtual memory space and found that there are too many 4MB chunks. I thought that if just one page in the 4MB chunk lives long, the entire chunk cannot be freed. Therefore new chunk is created again and again. In my opinion, the vm_map_ram() function should be used for temporary mapping and/or short term memory mapping. Otherwise virtual memory is wasted. I am not sure if my opinion is correct. If it is, please add some warning message about the vm_map_ram(). ---8<--- Subject: [PATCH] mm: warning comment for vm_map_ram vm_map_ram can occur locking of virtual memory space because if only one page lives long in one vmap_block, it takes 4MB (1024-times more than one page) space. Change-Id: I6f5919848cf03788b5846b7d850d66e4d93ac39a Signed-off-by: Gioh Kim <gioh.kim@xxxxxxx> --- mm/vmalloc.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/mm/vmalloc.c b/mm/vmalloc.c index 0fdf968..2de1d1b 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -1083,6 +1083,10 @@ EXPORT_SYMBOL(vm_unmap_ram); * @node: prefer to allocate data structures on this node * @prot: memory protection to use. PAGE_KERNEL for regular RAM * + * This function should be used for TEMPORARY mapping. If just one page lives i + * long, it would occupy 4MB vm size permamently. 100 pages (just 400KB) could + * takes 400MB with bad luck. + * * Returns: a pointer to the address that has been mapped, or %NULL on failure */ void *vm_map_ram(struct page **pages, unsigned int count, int node, pgprot_t prot) -- 1.7.9.5 Gioh Kim / 김 기 오 Research Engineer Advanced OS Technology Team Software Platform R&D Lab. Mobile: 82-10-7322-5548 E-mail: gioh.kim@xxxxxxx 19, Yangjae-daero 11gil Seocho-gu, Seoul 137-130, Korea -- 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