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Re: [PATCH v2 fixed 08/16] util/mmap-alloc: Factor out calculation of pa
From: |
David Hildenbrand |
Subject: |
Re: [PATCH v2 fixed 08/16] util/mmap-alloc: Factor out calculation of pagesize to mmap_pagesize() |
Date: |
Wed, 26 Feb 2020 18:36:30 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 |
On 24.02.20 15:16, Murilo Opsfelder Araújo wrote:
> On Monday, February 24, 2020 7:57:03 AM -03 David Hildenbrand wrote:
>> On 24.02.20 11:50, David Hildenbrand wrote:
>>> On 19.02.20 23:46, Peter Xu wrote:
>>>> On Wed, Feb 12, 2020 at 02:42:46PM +0100, David Hildenbrand wrote:
>>>>> Factor it out and add a comment.
>>>>>
>>>>> Reviewed-by: Igor Kotrasinski <address@hidden>
>>>>> Acked-by: Murilo Opsfelder Araujo <address@hidden>
>>>>> Reviewed-by: Richard Henderson <address@hidden>
>>>>> Cc: "Michael S. Tsirkin" <address@hidden>
>>>>> Cc: Murilo Opsfelder Araujo <address@hidden>
>>>>> Cc: Greg Kurz <address@hidden>
>>>>> Cc: Eduardo Habkost <address@hidden>
>>>>> Cc: "Dr. David Alan Gilbert" <address@hidden>
>>>>> Cc: Igor Mammedov <address@hidden>
>>>>> Signed-off-by: David Hildenbrand <address@hidden>
>>>>> ---
>>>>>
>>>>> util/mmap-alloc.c | 21 ++++++++++++---------
>>>>> 1 file changed, 12 insertions(+), 9 deletions(-)
>>>>>
>>>>> diff --git a/util/mmap-alloc.c b/util/mmap-alloc.c
>>>>> index 27dcccd8ec..82f02a2cec 100644
>>>>> --- a/util/mmap-alloc.c
>>>>> +++ b/util/mmap-alloc.c
>>>>> @@ -82,17 +82,27 @@ size_t qemu_mempath_getpagesize(const char
>>>>> *mem_path)
>>>>>
>>>>> return qemu_real_host_page_size;
>>>>>
>>>>> }
>>>>>
>>>>> +static inline size_t mmap_pagesize(int fd)
>>>>> +{
>>>>> +#if defined(__powerpc64__) && defined(__linux__)
>>>>> + /* Mappings in the same segment must share the same page size */
>>>>> + return qemu_fd_getpagesize(fd);
>>>>> +#else
>>>>> + return qemu_real_host_page_size;
>>>>> +#endif
>>>>> +}
>>>>
>>>> Pure question: This will return 4K even for huge pages on x86, is this
>>>> what we want?
>>>
>>> (was asking myself the same question) I *think* it's intended. It's
>>> mainly only used to allocate one additional guard page. The callers of
>>> qemu_ram_mmap() make sure that the size is properly aligned (e.g., to
>>> huge pages).
>>>
>>> Of course, a 4k guard page is sufficient - unless we can't use that
>>> (special case for ppc64 here).
>>>
>>> Thanks!
>>
>> We could rename the function to mmap_guard_pagesize(), thoughts?
>
> The existing qemu_fd_getpagesize() already returns qemu_real_host_page_size
> for
> non-anonymous mappings (when fd == -1). I think this new mmap_pagesize()
> could
> be dropped in favor of qemu_fd_getpagesize().
>
> A side effect of this change would be guard page using a bit more memory for
> non-anonymous mapping. Could that be a problem?
>
> What do you think?
So, I'll stick to mmap_guard_pagesize() for now, but use the actual page
size (via qemu_fd_getpagesize()) in the new size asserts.
Thanks!
--
Thanks,
David / dhildenb
- Re: [PATCH v2 fixed 05/16] exec: Factor out setting ram settings (madvise ...) into qemu_ram_apply_settings(), (continued)
- [PATCH v2 fixed 07/16] exec: Drop "shared" parameter from ram_block_add(), David Hildenbrand, 2020/02/12
- [PATCH v2 fixed 08/16] util/mmap-alloc: Factor out calculation of pagesize to mmap_pagesize(), David Hildenbrand, 2020/02/12
- Re: [PATCH v2 fixed 08/16] util/mmap-alloc: Factor out calculation of pagesize to mmap_pagesize(), Peter Xu, 2020/02/19
- Re: [PATCH v2 fixed 08/16] util/mmap-alloc: Factor out calculation of pagesize to mmap_pagesize(), David Hildenbrand, 2020/02/24
- Re: [PATCH v2 fixed 08/16] util/mmap-alloc: Factor out calculation of pagesize to mmap_pagesize(), David Hildenbrand, 2020/02/24
- Re: [PATCH v2 fixed 08/16] util/mmap-alloc: Factor out calculation of pagesize to mmap_pagesize(), Murilo Opsfelder Araújo, 2020/02/24
- Re: [PATCH v2 fixed 08/16] util/mmap-alloc: Factor out calculation of pagesize to mmap_pagesize(), Murilo Opsfelder Araújo, 2020/02/24
- Re: [PATCH v2 fixed 08/16] util/mmap-alloc: Factor out calculation of pagesize to mmap_pagesize(), David Hildenbrand, 2020/02/24
- Re: [PATCH v2 fixed 08/16] util/mmap-alloc: Factor out calculation of pagesize to mmap_pagesize(),
David Hildenbrand <=
- Re: [PATCH v2 fixed 08/16] util/mmap-alloc: Factor out calculation of pagesize to mmap_pagesize(), Peter Xu, 2020/02/24
- Re: [PATCH v2 fixed 08/16] util/mmap-alloc: Factor out calculation of pagesize to mmap_pagesize(), David Hildenbrand, 2020/02/24
[PATCH v2 fixed 09/16] util/mmap-alloc: Factor out reserving of a memory region to mmap_reserve(), David Hildenbrand, 2020/02/12
[PATCH v2 fixed 10/16] util/mmap-alloc: Factor out populating of memory to mmap_populate(), David Hildenbrand, 2020/02/12
[PATCH v2 fixed 11/16] util/mmap-alloc: Prepare for resizable mmaps, David Hildenbrand, 2020/02/12