[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Qemu-devel] [PATCH v2 2/4] util/oslib-win32: indicate alignment for

From: David Hildenbrand
Subject: Re: [Qemu-devel] [PATCH v2 2/4] util/oslib-win32: indicate alignment for qemu_anon_ram_alloc()
Date: Fri, 29 Jun 2018 17:39:10 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0

On 29.06.2018 16:49, Igor Mammedov wrote:
> On Thu, 28 Jun 2018 14:14:15 +0200
> David Hildenbrand <address@hidden> wrote:
>> Let's set the alignment just like for the posix variant. This will
>> implicitly set the alignment of the underlying memory region and
>> therefore make memory_region_get_alignment(mr) return something > 0 for
>> all memory backends applicable to PCDIMM/NVDIMM.
>> This will allow us to drop special handling in pc.c for
>> memory_region_get_alignment(mr) == 0, as we can then assume that it is
>> always set (and AFAICS >= getpagesize()).
>> For pc in pc_memory_plug(), under Windows TARGET_PAGE_SIZE == getpagesize(),
>> therefore alignment of DIMMs will not change, and therefore also not the
>> guest physical memory layout.
> why not use QEMU_VMALLOC_ALIGN for consistency (on win => getpagesize())
> instead of TARGET_PAGE_SIZE like linux allocator does?

Sure we can do that, I wanted to match here exactly what has been
written in the comment.

> Also looking at FIXME comment it notes that VirtualAlloc might have 64K
> alignment (though I haven't found it in VirtualAlloc manual).
> If that's true then we might need set *align to it to avoid auto-picked
> address overlap with previous allocation (not really sure about it).

"To determine the size of a page and the allocation granularity on the
host computer, use the GetSystemInfo" [1]

"The size of the region, in bytes. If the lpAddress parameter is NULL,
this value is rounded up to the next page boundary. " [1]

Historically, this seems to be 64k. But it will always be at least 4k
(page size). So what we could do is query the actual allocation granularity:

int get_allocation_granularity(void) {
        SYSTEM_INFO system_info;

        return system_info.dwAllocationGranularity

"dwAllocationGranularity: The granularity for the starting address at
which virtual memory can be allocated. For more information, see
VirtualAlloc." [2]

What do you think?

>> For spapr in spapr_memory_plug(), an alignment of 0 would have been used
> note that align == 0 would lead to crash where QEMU_ALIGN_UP() is used,
> so we don't care to keep it compatible (the same like in commit 92a37a04d)

Good point!




David / dhildenb

reply via email to

[Prev in Thread] Current Thread [Next in Thread]