Igor Mammedov <imammedo@xxxxxxxxxx> writes:
> Fallback might affect guest or worse whole host performance
> or functionality if backing file were used to share guest RAM
> with another process.
>
> Patch deprecates fallback so that we could remove it in future
> and ensure that QEMU will provide expected behavior and fail if
> it can't use user provided backing file.
>
> Signed-off-by: Igor Mammedov <imammedo@xxxxxxxxxx>
> ---
> PS:
> Patch is written on top of
> [PATCH v4 0/3] numa: deprecate '-numa node, mem' and default memory distribution
> to avoid conflicts in qemu-deprecated.texi
>
> numa.c | 4 ++--
> qemu-deprecated.texi | 8 ++++++++
> 2 files changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/numa.c b/numa.c
> index 91a29138a2..53d67b8ad9 100644
> --- a/numa.c
> +++ b/numa.c
> @@ -494,8 +494,8 @@ static void allocate_system_memory_nonnuma(MemoryRegion *mr, Object *owner,
> if (mem_prealloc) {
> exit(1);
> }
> - error_report("falling back to regular RAM allocation.");
> -
> + warn_report("falling back to regular RAM allocation. "
> + "Fallback to RAM allocation is deprecated.");
Can we give the user clues on how to avoid the deprecated fallback?
Warning message nitpick: the message should be a single phrase, with no
newline or trailing punctuation. Suggest something like
warn_report("falling back to regular RAM allocation");
error_printf("This is deprecated. <Advice on what\n"
"to do goes here>\n");
> /* Legacy behavior: if allocation failed, fall back to
> * regular RAM allocation.
> */
> diff --git a/qemu-deprecated.texi b/qemu-deprecated.texi
> index 2fe9b72121..2193705644 100644
> --- a/qemu-deprecated.texi
> +++ b/qemu-deprecated.texi
> @@ -112,6 +112,14 @@ QEMU using implicit generic or board specific splitting rule.
> Use @option{memdev} with @var{memory-backend-ram} backend or @option{mem} (if
> it's supported by used machine type) to define mapping explictly instead.
>
> +@subsection -mem-path fallback to RAM (since 4.1)
> +Currently if system memory allocation from file pointed by @option{mem-path}
> +fails, QEMU fallbacks to allocating from anonymous RAM. Which might result
> +in unpredictable behavior since provided backing file wasn't used.
Noch such verb "to fallback", obvious fix "QEMU falls back to"
Suggest "RAM, which might".
Better: "since the backing file specified by the user is ignored".
> In future
> +QEMU will not fallback and fail to start up, so user could fix his/her QEMU/host
> +configuration or explicitly use -m without -mem-path if system memory allocated
> +from anonymous RAM suits usecase.
What's "system memory allocation"?
Perhaps: "In the future, QEMU will not fall back, but fail instead.
Adjust either the host configuration [FIXME how?] or the QEMU
configuration [FIXME how?]."
> +
> @section QEMU Machine Protocol (QMP) commands
>
> @subsection block-dirty-bitmap-add "autoload" parameter (since 2.12.0)
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