On 21/08/17 14:31, David Gibson wrote: > On Fri, Aug 18, 2017 at 02:18:53PM +0100, Stefan Hajnoczi wrote: >> On Fri, Aug 18, 2017 at 03:39:20PM +1000, Alexey Kardashevskiy wrote: >>> ==94451== -------------------- 4 of 10 -------------------- >>> ==94451== max-live: 314,649,600 in 150 blocks >>> ==94451== tot-alloc: 314,649,600 in 150 blocks (avg size 2097664.00) >>> ==94451== deaths: none (none of these blocks were freed) >>> ==94451== acc-ratios: 0.00 rd, 0.00 wr (0 b-read, 0 b-written) >>> ==94451== at 0x4895600: memalign (in >>> /usr/lib/valgrind/vgpreload_exp-dhat-ppc64le-linux.so) >>> ==94451== by 0x48957E7: posix_memalign (in >>> /usr/lib/valgrind/vgpreload_exp-dhat-ppc64le-linux.so) >>> ==94451== by 0xB744AB: qemu_try_memalign (oslib-posix.c:106) >>> ==94451== by 0xA92053: qemu_try_blockalign (io.c:2493) >>> ==94451== by 0xA34DDF: qcow2_do_open (qcow2.c:1365) >>> ==94451== by 0xA35627: qcow2_open (qcow2.c:1526) >>> ==94451== by 0x9FB94F: bdrv_open_driver (block.c:1109) >>> ==94451== by 0x9FC413: bdrv_open_common (block.c:1365) >>> ==94451== by 0x9FF823: bdrv_open_inherit (block.c:2542) >>> ==94451== by 0x9FFC17: bdrv_open (block.c:2626) >>> ==94451== by 0xA71027: blk_new_open (block-backend.c:267) >>> ==94451== by 0x6D3E6B: blockdev_init (blockdev.c:588) >> >> This allocation is unnecessary. Most qcow2 files are not encrypted so >> s->cluster_data does not need to be allocated upfront. >> >> I'll send a patch. > > Is that sufficient to explain the problem, I can't quickly see how big > that unnecessary allocation is - but would it account for the 10s of > gigabytes usage we're seeing here? > > I'm suspecting we accidentally have a O(n^2) or worse space complexity > going on here. >
No, it is a small fraction only. See "[PATCH] qcow2: allocate cluster_cache/cluster_data on demand" thread for more details. -- Alexey
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