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Tsirkin" , Jason Wang , Stefan Hajnoczi , Stefano Garzarella , Germano Veit Michel , Raphael Norwitz Subject: [PATCH v1 12/15] libvhost-user: Use most of mmap_offset as fd_offset Date: Fri, 2 Feb 2024 22:53:29 +0100 Message-ID: <20240202215332.118728-13-david@redhat.com> In-Reply-To: <20240202215332.118728-1-david@redhat.com> References: <20240202215332.118728-1-david@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.6 Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=170.10.133.124; envelope-from=david@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -43 X-Spam_score: -4.4 X-Spam_bar: ---- X-Spam_report: (-4.4 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-2.276, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, T_SCC_BODY_TEXT_LINE=-0.01, T_SPF_TEMPERROR=0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZohoMail-DKIM: pass (identity @redhat.com) X-ZM-MESSAGEID: 1706910970289100009 Content-Type: text/plain; charset="utf-8" In the past, QEMU would create memory regions that could partially cover hugetlb pages, making mmap() fail if we would use the mmap_offset as an fd_offset. For that reason, we never used the mmap_offset as an offset into the fd and instead always mapped the fd from the very start. However, that can easily result in us mmap'ing a lot of unnecessary parts of an fd, possibly repeatedly. QEMU nowadays does not create memory regions that partially cover huge pages -- it never really worked with postcopy. QEMU handles merging of regions that partially cover huge pages (due to holes in boot memory) since 2018 in c1ece84e7c93 ("vhost: Huge page align and merge"). Let's be a bit careful and not unconditionally convert the mmap_offset into an fd_offset. Instead, let's simply detect the hugetlb size and pass as much as we can as fd_offset, making sure that we call mmap() with a properly aligned offset. With QEMU and a virtio-mem device that is fully plugged (50GiB using 50 memslots) the qemu-storage daemon process consumes in the VA space 1281GiB before this change and 58GiB after this change. Example debug output: =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D Vhost user message =3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D Request: VHOST_USER_ADD_MEM_REG (37) Flags: 0x9 Size: 40 Fds: 59 Adding region 50 guest_phys_addr: 0x0000000d80000000 memory_size: 0x0000000040000000 userspace_addr 0x00007f54ebffe000 mmap_offset 0x0000000c00000000 fd_offset: 0x0000000c00000000 new mmap_offset: 0x0000000000000000 mmap_addr: 0x00007f7ecc000000 Successfully added new region =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D Vhost user message =3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D Request: VHOST_USER_ADD_MEM_REG (37) Flags: 0x9 Size: 40 Fds: 59 Adding region 51 guest_phys_addr: 0x0000000dc0000000 memory_size: 0x0000000040000000 userspace_addr 0x00007f552bffe000 mmap_offset 0x0000000c40000000 fd_offset: 0x0000000c40000000 new mmap_offset: 0x0000000000000000 mmap_addr: 0x00007f7e8c000000 Successfully added new region Signed-off-by: David Hildenbrand Reviewed-by: Raphael Norwitz --- subprojects/libvhost-user/libvhost-user.c | 50 ++++++++++++++++++++--- 1 file changed, 45 insertions(+), 5 deletions(-) diff --git a/subprojects/libvhost-user/libvhost-user.c b/subprojects/libvho= st-user/libvhost-user.c index 75e47b7bb3..7d8293dc84 100644 --- a/subprojects/libvhost-user/libvhost-user.c +++ b/subprojects/libvhost-user/libvhost-user.c @@ -43,6 +43,8 @@ #include #include #include +#include +#include =20 #ifdef __NR_userfaultfd #include @@ -281,12 +283,36 @@ vu_remove_all_mem_regs(VuDev *dev) dev->nregions =3D 0; } =20 +static size_t +get_fd_pagesize(int fd) +{ + static size_t pagesize; +#if defined(__linux__) + struct statfs fs; + int ret; + + do { + ret =3D fstatfs(fd, &fs); + } while (ret !=3D 0 && errno =3D=3D EINTR); + + if (!ret && fs.f_type =3D=3D HUGETLBFS_MAGIC) { + return fs.f_bsize; + } +#endif + + if (!pagesize) { + pagesize =3D getpagesize(); + } + return pagesize; +} + static void _vu_add_mem_reg(VuDev *dev, VhostUserMemoryRegion *msg_region, int fd) { const uint64_t start_gpa =3D msg_region->guest_phys_addr; const uint64_t end_gpa =3D start_gpa + msg_region->memory_size; int prot =3D PROT_READ | PROT_WRITE; + uint64_t mmap_offset, fd_offset; VuDevRegion *r; void *mmap_addr; int low =3D 0; @@ -335,11 +361,25 @@ _vu_add_mem_reg(VuDev *dev, VhostUserMemoryRegion *ms= g_region, int fd) idx =3D low; =20 /* - * We don't use offset argument of mmap() since the mapped address has - * to be page aligned, and we use huge pages. + * Convert most of msg_region->mmap_offset to fd_offset. In almost all + * cases, this will leave us with mmap_offset =3D=3D 0, mmap()'ing only + * what we really need. Only if a memory region would partially cover + * hugetlb pages, we'd get mmap_offset !=3D 0, which usually doesn't h= appen + * anymore (i.e., modern QEMU). + * + * Note that mmap() with hugetlb would fail if the offset into the file + * is not aligned to the huge page size. */ - mmap_addr =3D mmap(0, msg_region->memory_size + msg_region->mmap_offse= t, - prot, MAP_SHARED | MAP_NORESERVE, fd, 0); + fd_offset =3D ALIGN_DOWN(msg_region->mmap_offset, get_fd_pagesize(fd)); + mmap_offset =3D msg_region->mmap_offset - fd_offset; + + DPRINT(" fd_offset: 0x%016"PRIx64"\n", + fd_offset); + DPRINT(" adj mmap_offset: 0x%016"PRIx64"\n", + mmap_offset); + + mmap_addr =3D mmap(0, msg_region->memory_size + mmap_offset, + prot, MAP_SHARED | MAP_NORESERVE, fd, fd_offset); if (mmap_addr =3D=3D MAP_FAILED) { vu_panic(dev, "region mmap error: %s", strerror(errno)); return; @@ -354,7 +394,7 @@ _vu_add_mem_reg(VuDev *dev, VhostUserMemoryRegion *msg_= region, int fd) r->size =3D msg_region->memory_size; r->qva =3D msg_region->userspace_addr; r->mmap_addr =3D (uint64_t)(uintptr_t)mmap_addr; - r->mmap_offset =3D msg_region->mmap_offset; + r->mmap_offset =3D mmap_offset; dev->nregions++; =20 if (dev->postcopy_listening) { --=20 2.43.0