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authorBrian Norris <computersforpeace@gmail.com>2012-02-10 20:35:05 -0800
committerArtem Bityutskiy <artem.bityutskiy@linux.intel.com>2012-02-14 11:01:20 +0200
commit71c76e74661492b4f68f670514866cfc85f47089 (patch)
treecda9005c70100f4a343ac25fd768369c6ba523a8 /tests/checkfs/README
parentb989a29c2c1159867e03356d49a2903431899159 (diff)
libmtd: fix mtd_write() issues for large data-only writes
ioctl(MEMWRITE) is implemented with memdup_user(), and so it allocates kernel memory in contiguous regions. This limits its usefulness for large amounts of data, since contiguous kernel memory can become scarce. I have experienced "out of memory" problems with ubiformat, for instance, which writes in eraseblock-sized regions: ... ubiformat: flashing eraseblock 12 -- 72 % complete ubiformat: page allocation failure. order:8, mode:0xd0 Call Trace: [<8043fa7c>] dump_stack+0x8/0x34 [<8008c940>] __alloc_pages_nodemask+0x408/0x618 [<800bd748>] cache_alloc_refill+0x400/0x730 [<800bdbbc>] __kmalloc+0x144/0x154 [<8009cae4>] memdup_user+0x24/0x94 [<802d04e4>] mtd_ioctl+0xba8/0xbd0 [<802d0544>] mtd_unlocked_ioctl+0x38/0x5c [<800d43c0>] do_vfs_ioctl+0xa4/0x6e4 [<800d4a44>] sys_ioctl+0x44/0xa0 [<8000f95c>] stack_done+0x20/0x40 ... libmtd: error!: MEMWRITE ioctl failed for eraseblock 12 (mtd0) error 12 (Cannot allocate memory) ubiformat: error!: cannot write eraseblock 12 error 12 (Cannot allocate memory) This error can be mitigated for now by only using ioctl(MEMWRITE) when we need to write OOB data, since we can only do this in small transactions anyway. Then, data-only transactions (like those originating from ubiformat) can be carried out with write() calls. This issue can also be solved within the kernel ioctl(), but either way, this patch is still useful, since write() is more straightforward (and efficient?) than ioctl() for data-only writes. Signed-off-by: Brian Norris <computersforpeace@gmail.com> Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
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