Re: [Qemu-block] [PATCH] qcow2: Fix the calculation of the maximum L2 cache size

2019-08-18 Thread Leonid Bloch
Thanks, Berto! On 8/16/19 3:17 PM, Alberto Garcia wrote: > The size of the qcow2 L2 cache defaults to 32 MB, which can be easily > larger than the maximum amount of L2 metadata that the image can have. > For example: with 64 KB clusters the user would need a qcow2 image > with a virtual size of 25

Re: [Qemu-block] [PATCH] qcow2: Fix the calculation of the maximum L2 cache size

2019-08-16 Thread Alberto Garcia
On Fri 16 Aug 2019 04:08:19 PM CEST, Kevin Wolf wrote: >> And yes, the odd value on the 512KB row on that we discussed last month >> is due to this same bug: >> >> https://lists.gnu.org/archive/html/qemu-block/2019-07/msg00496.html > > Hm... And suddently it makes sense. :-) > > So I assume all of

Re: [Qemu-block] [PATCH] qcow2: Fix the calculation of the maximum L2 cache size

2019-08-16 Thread Kevin Wolf
Am 16.08.2019 um 15:30 hat Alberto Garcia geschrieben: > On Fri 16 Aug 2019 02:59:21 PM CEST, Kevin Wolf wrote: > > The requirement so that this bug doesn't affect the user seems to be > > that the image size is a multiple of 64k * 8k = 512 MB. Which means > > that users are probably often lucky en

Re: [Qemu-block] [PATCH] qcow2: Fix the calculation of the maximum L2 cache size

2019-08-16 Thread Alberto Garcia
On Fri 16 Aug 2019 02:59:21 PM CEST, Kevin Wolf wrote: > The requirement so that this bug doesn't affect the user seems to be > that the image size is a multiple of 64k * 8k = 512 MB. Which means > that users are probably often lucky enough in practice. Or rather: cluster_size^2 / 8, which, if my

Re: [Qemu-block] [PATCH] qcow2: Fix the calculation of the maximum L2 cache size

2019-08-16 Thread Kevin Wolf
Am 16.08.2019 um 14:17 hat Alberto Garcia geschrieben: > The size of the qcow2 L2 cache defaults to 32 MB, which can be easily > larger than the maximum amount of L2 metadata that the image can have. > For example: with 64 KB clusters the user would need a qcow2 image > with a virtual size of 256 G

Re: [Qemu-block] [PATCH] qcow2: Fix the calculation of the maximum L2 cache size

2019-08-16 Thread Alberto Garcia
Cc qemu-stable This bug means that under certain conditions it's impossible to create a cache large enough for the image, resulting in reduced I/O performance. On Fri, Aug 16, 2019 at 03:17:42PM +0300, Alberto Garcia wrote: > The size of the qcow2 L2 cache defaults to 32 MB, which can be easily >

[Qemu-block] [PATCH] qcow2: Fix the calculation of the maximum L2 cache size

2019-08-16 Thread Alberto Garcia
The size of the qcow2 L2 cache defaults to 32 MB, which can be easily larger than the maximum amount of L2 metadata that the image can have. For example: with 64 KB clusters the user would need a qcow2 image with a virtual size of 256 GB in order to have 32 MB of L2 metadata. Because of that, sinc