| Message ID | 20170829213657.GO27715@localhost.localdomain |
|---|---|
| State | New |
| Headers | show |
| Series | fixup! hostmem-file: Add "discard-data" option | expand |
On Tue, Aug 29, 2017 at 06:36:57PM -0300, Eduardo Habkost wrote: > On Tue, Aug 29, 2017 at 10:12:58AM -0300, Eduardo Habkost wrote: > > On Tue, Aug 29, 2017 at 12:13:45PM +0100, Daniel P. Berrange wrote: > > > On Thu, Aug 24, 2017 at 04:23:15PM -0300, Eduardo Habkost wrote: > [...] > > > > @@ -4172,6 +4172,9 @@ the path to either a shared memory or huge page filesystem mount. > > > > The @option{share} boolean option determines whether the memory > > > > region is marked as private to QEMU, or shared. The latter allows > > > > a co-operating external process to access the QEMU memory region. > > > > +Setting the @option{discard-data} boolean option to @var{on} > > > > +indicates that file contents can be destroyed when QEMU exits, > > > > +to avoid unnecessarily flushing data to the backing file. > > > > > > We should note that this only works if QEMU shuts down normally. If QEMU > > > is aggressively killed (SIGKILL) or aborts for some reason, then we'll > > > never get a chance to invoke madvise(), so presumably the kernel will > > > still flush the data > > > > Good point. I tried to not give any guarantees by saying > > "contents _can_ be destroyed", but users may still have different > > expectations. > > > > I will change it to: > > > > Setting the @option{discard-data} boolean option to @var{on} > > indicates that file contents can be destroyed when QEMU exits, > > to avoid unnecessarily flushing data to the backing file. Note > > that @option{discard-data} is only an optimization, and QEMU > > might not discard file contents if it aborts unexpectedly or is > > terminated using SIGKILL. > > Fixup patch: > > Signed-off-by: Eduardo Habkost <ehabkost@redhat.com> > --- > qemu-options.hx | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > diff --git a/qemu-options.hx b/qemu-options.hx > index ad985e4..de9a18a 100644 > --- a/qemu-options.hx > +++ b/qemu-options.hx > @@ -4174,7 +4174,10 @@ region is marked as private to QEMU, or shared. The latter allows > a co-operating external process to access the QEMU memory region. > Setting the @option{discard-data} boolean option to @var{on} > indicates that file contents can be destroyed when QEMU exits, > -to avoid unnecessarily flushing data to the backing file. > +to avoid unnecessarily flushing data to the backing file. Note > +that @option{discard-data} is only an optimization, and QEMU > +might not discard file contents if it aborts unexpectedly or is > +terminated using SIGKILL. > > @item -object rng-random,id=@var{id},filename=@var{/dev/random} For the combined patch: Reviewed-by: Daniel P. Berrange <berrange@redhat.com> Regards, Daniel
diff --git a/qemu-options.hx b/qemu-options.hx index ad985e4..de9a18a 100644 --- a/qemu-options.hx +++ b/qemu-options.hx @@ -4174,7 +4174,10 @@ region is marked as private to QEMU, or shared. The latter allows a co-operating external process to access the QEMU memory region. Setting the @option{discard-data} boolean option to @var{on} indicates that file contents can be destroyed when QEMU exits, -to avoid unnecessarily flushing data to the backing file. +to avoid unnecessarily flushing data to the backing file. Note +that @option{discard-data} is only an optimization, and QEMU +might not discard file contents if it aborts unexpectedly or is +terminated using SIGKILL. @item -object rng-random,id=@var{id},filename=@var{/dev/random}