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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1 MIME-Version: 1.0 In-Reply-To: <5327048.DvuYhMxLoT@kermit.br.ibm.com> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-MC-Unique: oLP1adDKOCOU8nVCWwelvQ-1 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 205.139.110.120 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Eduardo Habkost , "Michael S . Tsirkin" , qemu-devel@nongnu.org, "Dr . David Alan Gilbert" , Greg Kurz , Paolo Bonzini , Richard Henderson Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" >> /* we can only map whole pages */ >> - size =3D QEMU_ALIGN_UP(size, pagesize); >> + old_size =3D QEMU_ALIGN_UP(old_size, pagesize); >> + new_size =3D QEMU_ALIGN_UP(new_size, pagesize); >=20 > Shouldn't we just assert old_size and new_size are aligned with > pagesize? >=20 Already reworked :) >> + >> + /* we support actually resizable memory regions only on Linux */ >> + if (old_size < new_size) { >> + /* populate the missing piece into the reserved area */ >> + ptr =3D mmap_populate(ptr + old_size, new_size - old_size, fd, >> old_size, + shared, is_pmem); >> + } else if (old_size > new_size) { >> + /* discard this piece, keeping the area reserved (should never >> fail) */ + ptr =3D mmap_reserve(ptr + new_size, old_size - new_si= ze, >> fd); + } >=20 > I find the behaviour of this function somewhat confusing. Perhaps I'm > missing something and need your help to clarify. Please bear with me. >=20 > For the case where we want to grow in size, it returns a populated area > (PROT_READ | PROT_WRITE flags). >=20 > And for the case where we want to shrink in size, it returns a reserved > area (PROT_NONE flag), requiring the caller to call mmap_populate() > again to be able to use that memory. >=20 > I believe the behaviour should be consistent regardless if we want to > grow or shrink in size. Either return a reserved or an already > populated area. Not both. The return value is only used to differentiate between success (!=3D MAP_FAILED) and failure (=3D=3D MAP_FAILED), nothing else. For now, I switched to returning a bool instead (resized vs. not resized), that avoids this inconsistency. See my reply to Richard's comment= . >=20 > Would "old_size =3D=3D new_size" situation be possible? In this case, pt= r > would be returned without changing protection flags of the mapping. It could, although in this patch set, it never would :) The result would be a NOP, which is the right thing to do. >=20 > Shouldn't we also assert that new_size <=3D max_size? Then we would have to pass max_size, just for asserting. I'll leave that to the callers for now. >=20 >> + return ptr; >> +} >> + >> +void qemu_ram_munmap(int fd, void *ptr, size_t max_size) >> +{ >> + const size_t pagesize =3D mmap_pagesize(fd); >> + >> + /* we can only map whole pages */ >> + max_size =3D QEMU_ALIGN_UP(max_size, pagesize); >=20 > Shouldn't we just assert this and leave the alignment to the caller? Already reworked. Thanks! --=20 Thanks, David / dhildenb