On 06.02.20 00:00, Murilo Opsfelder Araújo wrote:
> Hello, David.
>
> On Monday, February 3, 2020 3:31:20 PM -03 David Hildenbrand wrote:
>> When shrinking a mmap we want to re-reserve the already populated area.
>> When growing a memory region, we want to populate starting with a given
>> fd_offset. Prepare by allowing to pass these parameters.
>>
>> Also, let's make sure we always process full pages, to avoid
>> unmapping/remapping pages that are already in use when
>> growing/shrinking. (existing callers seem to guarantee this, but that's
>> not obvious)
>>
>> Cc: "Michael S. Tsirkin" <m...@redhat.com>
>> Cc: Greg Kurz <gr...@kaod.org>
>> Cc: Murilo Opsfelder Araujo <muri...@linux.ibm.com>
>> Cc: Eduardo Habkost <ehabk...@redhat.com>
>> Cc: "Dr. David Alan Gilbert" <dgilb...@redhat.com>
>> Signed-off-by: David Hildenbrand <da...@redhat.com>
>> ---
>> util/mmap-alloc.c | 32 +++++++++++++++++++++-----------
>> 1 file changed, 21 insertions(+), 11 deletions(-)
>>
>> diff --git a/util/mmap-alloc.c b/util/mmap-alloc.c
>> index f043ccb0ab..63ad6893b7 100644
>> --- a/util/mmap-alloc.c
>> +++ b/util/mmap-alloc.c
>> @@ -83,12 +83,12 @@ size_t qemu_mempath_getpagesize(const char *mem_path)
>> }
>>
>> /*
>> - * Reserve a new memory region of the requested size to be used for mapping
>> - * from the given fd (if any).
>> + * Reserve a new memory region of the requested size or re-reserve parts
>> + * of an existing region to be used for mapping from the given fd (if any).
>> */
>> -static void *mmap_reserve(size_t size, int fd)
>> +static void *mmap_reserve(void *ptr, size_t size, int fd)
>> {
>> - int flags = MAP_PRIVATE;
>> + int flags = MAP_PRIVATE | (ptr ? MAP_FIXED : 0);
>>
>> #if defined(__powerpc64__) && defined(__linux__)
>> /*
>> @@ -111,19 +111,23 @@ static void *mmap_reserve(size_t size, int fd)
>> flags |= MAP_ANONYMOUS;
>> #endif
>>
>> - return mmap(0, size, PROT_NONE, flags, fd, 0);
>> + return mmap(ptr, size, PROT_NONE, flags, fd, 0);
>> }
>>
>> /*
>> * Populate memory in a reserved region from the given fd (if any).
>> */
>> -static void *mmap_populate(void *ptr, size_t size, int fd, bool shared,
>> - bool is_pmem)
>> +static void *mmap_populate(void *ptr, size_t size, int fd, size_t
>> fd_offset, + bool shared, bool is_pmem)
>> {
>> int map_sync_flags = 0;
>> int flags = MAP_FIXED;
>> void *new_ptr;
>>
>> + if (fd == -1) {
>> + fd_offset = 0;
>> + }
>> +
>> flags |= fd == -1 ? MAP_ANONYMOUS : 0;
>> flags |= shared ? MAP_SHARED : MAP_PRIVATE;
>> if (shared && is_pmem) {
>> @@ -131,7 +135,7 @@ static void *mmap_populate(void *ptr, size_t size, int
>> fd, bool shared, }
>>
>> new_ptr = mmap(ptr, size, PROT_READ | PROT_WRITE, flags |
>> map_sync_flags, - fd, 0);
>> + fd, fd_offset);
>> if (new_ptr == MAP_FAILED && map_sync_flags) {
>> if (errno == ENOTSUP) {
>> char *proc_link = g_strdup_printf("/proc/self/fd/%d", fd);
>> @@ -153,7 +157,7 @@ static void *mmap_populate(void *ptr, size_t size, int
>> fd, bool shared, * If mmap failed with MAP_SHARED_VALIDATE | MAP_SYNC, we
>> will try * again without these flags to handle backwards compatibility. */
>> - new_ptr = mmap(ptr, size, PROT_READ | PROT_WRITE, flags, fd, 0);
>> + new_ptr = mmap(ptr, size, PROT_READ | PROT_WRITE, flags, fd,
>> fd_offset); }
>> return new_ptr;
>> }
>> @@ -178,13 +182,16 @@ void *qemu_ram_mmap(int fd,
>> size_t offset, total;
>> void *ptr, *guardptr;
>>
>> + /* we can only map whole pages */
>> + size = QEMU_ALIGN_UP(size, pagesize);
>> +
>
> Caller already rounds up size to block->page_size.
>
> Why this QEMU_ALIGN_UP is necessary?
Thanks for having a look
I guess you read the patch description, right? :)
"(existing callers seem to guarantee this, but that's
not obvious)"
Do you prefer a g_assert(IS_ALIGNED()) instead?
Thanks!
--
Thanks,
David / dhildenb
