[Qemu-devel] [PATCHv3 for-2.13 0/2] Helpers to obtain host page sizes for guest RAM

[Qemu-devel] [PATCHv3 for-2.13 0/2] Helpers to obtain host page sizes for guest RAM

[David Gibson]

This series makes some small changes to make it easier to obtain the
host page size backing given portions of guest RAM.  We use this in a
couple of places currently, and I have one or two more to add in some
upcoming code.

Assuming there are no objections, what should be the procedure for
staging this?  Can I put it in my for-2.13 ppc tree, even though it's
technically generic code, or should it go through someone else's tree?

Changes since v2:
  * Corrected grammar error in commit message
  * Correct build error on non-linux hosts
Changes since v1:
  * Reworked design based on Eduardo's feedback
  * Split into two patches

David Gibson (2):
  Make qemu_mempath_getpagesize() accept NULL
  Add host_memory_backend_pagesize() helper

 backends/hostmem.c       | 18 ++++++++++++++++++
 exec.c                   | 20 +++++---------------
 include/sysemu/hostmem.h |  2 ++
 target/ppc/kvm.c         | 10 +---------
 util/mmap-alloc.c        | 26 ++++++++++++++------------
 5 files changed, 40 insertions(+), 36 deletions(-)

-- 
2.14.3

[Qemu-devel] [PATCHv3 for-2.13 1/2] Make qemu_mempath_getpagesize() accept NULL

[David Gibson]

qemu_mempath_getpagesize() gets the effective (host side) page size for
a block of memory backed by an mmap()ed file on the host.  It requires
the mem_path parameter to be non-NULL.

This ends up meaning all the callers need a different case for handling
anonymous memory (for memory-backend-ram or default memory with -mem-path
is not specified).

We can make all those callers a little simpler by having
qemu_mempath_getpagesize() accept NULL, and treat that as the anonymous
memory case.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Greg Kurz <groug@kaod.org>
---
 exec.c            | 21 ++++++---------------
 target/ppc/kvm.c  |  8 ++------
 util/mmap-alloc.c | 26 ++++++++++++++------------
 3 files changed, 22 insertions(+), 33 deletions(-)

diff --git a/exec.c b/exec.c
index 02b1efebb7..b38b004563 100644
--- a/exec.c
+++ b/exec.c
@@ -1488,19 +1488,14 @@ void ram_block_dump(Monitor *mon)
  */
 static int find_max_supported_pagesize(Object *obj, void *opaque)
 {
-    char *mem_path;
     long *hpsize_min = opaque;
 
     if (object_dynamic_cast(obj, TYPE_MEMORY_BACKEND)) {
-        mem_path = object_property_get_str(obj, "mem-path", NULL);
-        if (mem_path) {
-            long hpsize = qemu_mempath_getpagesize(mem_path);
-            g_free(mem_path);
-            if (hpsize < *hpsize_min) {
-                *hpsize_min = hpsize;
-            }
-        } else {
-            *hpsize_min = getpagesize();
+        char *mem_path = object_property_get_str(obj, "mem-path", NULL);
+        long hpsize = qemu_mempath_getpagesize(mem_path);
+        g_free(mem_path);
+        if (hpsize < *hpsize_min) {
+            *hpsize_min = hpsize;
         }
     }
 
@@ -1513,11 +1508,7 @@ long qemu_getrampagesize(void)
     long mainrampagesize;
     Object *memdev_root;
 
-    if (mem_path) {
-        mainrampagesize = qemu_mempath_getpagesize(mem_path);
-    } else {
-        mainrampagesize = getpagesize();
-    }
+    mainrampagesize = qemu_mempath_getpagesize(mem_path);
 
     /* it's possible we have memory-backend objects with
      * hugepage-backed RAM. these may get mapped into system
diff --git a/target/ppc/kvm.c b/target/ppc/kvm.c
index 79a436a384..e24fa50dc9 100644
--- a/target/ppc/kvm.c
+++ b/target/ppc/kvm.c
@@ -499,12 +499,8 @@ bool kvmppc_is_mem_backend_page_size_ok(const char *obj_path)
     char *mempath = object_property_get_str(mem_obj, "mem-path", NULL);
     long pagesize;
 
-    if (mempath) {
-        pagesize = qemu_mempath_getpagesize(mempath);
-        g_free(mempath);
-    } else {
-        pagesize = getpagesize();
-    }
+    pagesize = qemu_mempath_getpagesize(mempath);
+    g_free(mempath);
 
     return pagesize >= max_cpu_page_size;
 }
diff --git a/util/mmap-alloc.c b/util/mmap-alloc.c
index 2fd8cbcc6f..fd329eccd8 100644
--- a/util/mmap-alloc.c
+++ b/util/mmap-alloc.c
@@ -50,19 +50,21 @@ size_t qemu_mempath_getpagesize(const char *mem_path)
     struct statfs fs;
     int ret;
 
-    do {
-        ret = statfs(mem_path, &fs);
-    } while (ret != 0 && errno == EINTR);
-
-    if (ret != 0) {
-        fprintf(stderr, "Couldn't statfs() memory path: %s\n",
-                strerror(errno));
-        exit(1);
-    }
+    if (mem_path) {
+        do {
+            ret = statfs(mem_path, &fs);
+        } while (ret != 0 && errno == EINTR);
 
-    if (fs.f_type == HUGETLBFS_MAGIC) {
-        /* It's hugepage, return the huge page size */
-        return fs.f_bsize;
+        if (ret != 0) {
+            fprintf(stderr, "Couldn't statfs() memory path: %s\n",
+                    strerror(errno));
+            exit(1);
+        }
+
+        if (fs.f_type == HUGETLBFS_MAGIC) {
+            /* It's hugepage, return the huge page size */
+            return fs.f_bsize;
+        }
     }
 #ifdef __sparc__
     /* SPARC Linux needs greater alignment than the pagesize */
-- 
2.14.3

[Qemu-devel] [PATCHv3 for-2.13 2/2] Add host_memory_backend_pagesize() helper

[David Gibson]

There are a couple places (one generic, one target specific) where we need
to get the host page size associated with a particular memory backend.  I
have some upcoming code which will add another place which wants this.  So,
for convenience, add a helper function to calculate this.

host_memory_backend_pagesize() returns the host pagesize for a given
HostMemoryBackend object.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Greg Kurz <groug@kaod.org>
---
 backends/hostmem.c       | 18 ++++++++++++++++++
 exec.c                   |  5 ++---
 include/sysemu/hostmem.h |  2 ++
 target/ppc/kvm.c         |  6 +-----
 4 files changed, 23 insertions(+), 8 deletions(-)

diff --git a/backends/hostmem.c b/backends/hostmem.c
index f61093654e..6a0c474222 100644
--- a/backends/hostmem.c
+++ b/backends/hostmem.c
@@ -18,6 +18,7 @@
 #include "qapi/visitor.h"
 #include "qemu/config-file.h"
 #include "qom/object_interfaces.h"
+#include "qemu/mmap-alloc.h"
 
 #ifdef CONFIG_NUMA
 #include <numaif.h>
@@ -262,6 +263,23 @@ bool host_memory_backend_is_mapped(HostMemoryBackend *backend)
     return backend->is_mapped;
 }
 
+#ifdef __linux__
+size_t host_memory_backend_pagesize(HostMemoryBackend *memdev)
+{
+    Object *obj = OBJECT(memdev);
+    char *path = object_property_get_str(obj, "mem-path", NULL);
+    size_t pagesize = qemu_mempath_getpagesize(path);
+
+    g_free(path);
+    return pagesize;
+}
+#else
+size_t host_memory_backend_pagesize(HostMemoryBackend *memdev)
+{
+    return getpagesize();
+}
+#endif
+
 static void
 host_memory_backend_memory_complete(UserCreatable *uc, Error **errp)
 {
diff --git a/exec.c b/exec.c
index b38b004563..c7fcefa851 100644
--- a/exec.c
+++ b/exec.c
@@ -1491,9 +1491,8 @@ static int find_max_supported_pagesize(Object *obj, void *opaque)
     long *hpsize_min = opaque;
 
     if (object_dynamic_cast(obj, TYPE_MEMORY_BACKEND)) {
-        char *mem_path = object_property_get_str(obj, "mem-path", NULL);
-        long hpsize = qemu_mempath_getpagesize(mem_path);
-        g_free(mem_path);
+        long hpsize = host_memory_backend_pagesize(MEMORY_BACKEND(obj));
+
         if (hpsize < *hpsize_min) {
             *hpsize_min = hpsize;
         }
diff --git a/include/sysemu/hostmem.h b/include/sysemu/hostmem.h
index 47bc9846ac..bc36899bb8 100644
--- a/include/sysemu/hostmem.h
+++ b/include/sysemu/hostmem.h
@@ -68,4 +68,6 @@ MemoryRegion *host_memory_backend_get_memory(HostMemoryBackend *backend,
 
 void host_memory_backend_set_mapped(HostMemoryBackend *backend, bool mapped);
 bool host_memory_backend_is_mapped(HostMemoryBackend *backend);
+size_t host_memory_backend_pagesize(HostMemoryBackend *memdev);
+
 #endif
diff --git a/target/ppc/kvm.c b/target/ppc/kvm.c
index e24fa50dc9..f62f7ac288 100644
--- a/target/ppc/kvm.c
+++ b/target/ppc/kvm.c
@@ -496,11 +496,7 @@ static void kvm_fixup_page_sizes(PowerPCCPU *cpu)
 bool kvmppc_is_mem_backend_page_size_ok(const char *obj_path)
 {
     Object *mem_obj = object_resolve_path(obj_path, NULL);
-    char *mempath = object_property_get_str(mem_obj, "mem-path", NULL);
-    long pagesize;
-
-    pagesize = qemu_mempath_getpagesize(mempath);
-    g_free(mempath);
+    long pagesize = host_memory_backend_pagesize(MEMORY_BACKEND(mem_obj));
 
     return pagesize >= max_cpu_page_size;
 }
-- 
2.14.3

Re: [Qemu-devel] [PATCHv3 for-2.13 0/2] Helpers to obtain host page sizes for guest RAM

[Paolo Bonzini]

On 11/04/2018 09:04, David Gibson wrote:
> This series makes some small changes to make it easier to obtain the
> host page size backing given portions of guest RAM.  We use this in a
> couple of places currently, and I have one or two more to add in some
> upcoming code.
> 
> Assuming there are no objections, what should be the procedure for
> staging this?  Can I put it in my for-2.13 ppc tree, even though it's
> technically generic code, or should it go through someone else's tree?

Yes, go ahead:

Acked-by: Paolo Bonzini <pbonzini@redhat.com>

Paolo

Re: [Qemu-devel] [PATCHv3 for-2.13 0/2] Helpers to obtain host page sizes for guest RAM

[David Gibson]

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On Wed, Apr 11, 2018 at 03:54:20PM +0200, Paolo Bonzini wrote:
> On 11/04/2018 09:04, David Gibson wrote:
> > This series makes some small changes to make it easier to obtain the
> > host page size backing given portions of guest RAM.  We use this in a
> > couple of places currently, and I have one or two more to add in some
> > upcoming code.
> > 
> > Assuming there are no objections, what should be the procedure for
> > staging this?  Can I put it in my for-2.13 ppc tree, even though it's
> > technically generic code, or should it go through someone else's tree?
> 
> Yes, go ahead:
> 
> Acked-by: Paolo Bonzini <pbonzini@redhat.com>

I'm assuming that's an ack to putting it through my tree.

In which case, done, thanks.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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