From: Florian Weimer <fw@deneb.enyo.de>
To: libc-alpha@sourceware.org
Subject: [PATCH] support: Add support_blob_repeat_allocate_shared
Date: Tue, 05 May 2020 15:55:19 +0200 [thread overview]
Message-ID: <87ftce1o6w.fsf@mid.deneb.enyo.de> (raw)
-----
support/blob_repeat.c | 31 +++++++++++++++++++++------
support/blob_repeat.h | 12 ++++++++++-
support/tst-support_blob_repeat.c | 45 ++++++++++++++++++++++++++++-----------
3 files changed, 68 insertions(+), 20 deletions(-)
diff --git a/support/blob_repeat.c b/support/blob_repeat.c
index a7aa9bf4c7..cd6297e026 100644
--- a/support/blob_repeat.c
+++ b/support/blob_repeat.c
@@ -125,10 +125,11 @@ minimum_stride_size (size_t page_size, size_t element_size)
}
/* Allocations larger than maximum_small_size potentially use mmap
- with alias mappings. */
+ with alias mappings. If SHARED, the alias mappings are created
+ using MAP_SHARED instead of MAP_PRIVATE. */
static struct support_blob_repeat
allocate_big (size_t total_size, const void *element, size_t element_size,
- size_t count)
+ size_t count, bool shared)
{
unsigned long page_size = xsysconf (_SC_PAGESIZE);
size_t stride_size = minimum_stride_size (page_size, element_size);
@@ -213,7 +214,11 @@ allocate_big (size_t total_size, const void *element, size_t element_size,
{
size_t remaining_size = total_size;
char *current = target;
- int flags = MAP_FIXED | MAP_FILE | MAP_PRIVATE;
+ int flags = MAP_FIXED | MAP_FILE;
+ if (shared)
+ flags |= MAP_SHARED;
+ else
+ flags |= MAP_PRIVATE;
#ifdef MAP_NORESERVE
flags |= MAP_NORESERVE;
#endif
@@ -251,8 +256,8 @@ allocate_big (size_t total_size, const void *element, size_t element_size,
}
struct support_blob_repeat
-support_blob_repeat_allocate (const void *element, size_t element_size,
- size_t count)
+repeat_allocate (const void *element, size_t element_size,
+ size_t count, bool shared)
{
size_t total_size;
if (__builtin_mul_overflow (element_size, count, &total_size))
@@ -263,7 +268,21 @@ support_blob_repeat_allocate (const void *element, size_t element_size,
if (total_size <= maximum_small_size)
return allocate_malloc (total_size, element, element_size, count);
else
- return allocate_big (total_size, element, element_size, count);
+ return allocate_big (total_size, element, element_size, count, shared);
+}
+
+struct support_blob_repeat
+support_blob_repeat_allocate (const void *element, size_t element_size,
+ size_t count)
+{
+ return repeat_allocate (element, element_size, count, false);
+}
+
+struct support_blob_repeat
+support_blob_repeat_allocate_shared (const void *element, size_t element_size,
+ size_t count)
+{
+ return repeat_allocate (element, element_size, count, true);
}
void
diff --git a/support/blob_repeat.h b/support/blob_repeat.h
index 12f33bcd02..519458cf50 100644
--- a/support/blob_repeat.h
+++ b/support/blob_repeat.h
@@ -38,7 +38,17 @@ struct support_blob_repeat support_blob_repeat_allocate (const void *element,
size_t element_size,
size_t count);
-/* Deallocate the blob created by support_blob_repeat_allocate. */
+/* Like support_blob_repeat_allocate, except that copy-on-write
+ semantics are disabled. This means writing to one part of the blob
+ can affect other parts. It is possible to map non-shared memory
+ over parts of the resulting blob using MAP_ANONYMOUS | MAP_FIXED
+ | MAP_PRIVATE, so that writes to these parts do not affect
+ others. */
+struct support_blob_repeat support_blob_repeat_allocate_shared
+ (const void *element, size_t element_size, size_t count);
+
+/* Deallocate the blob created by support_blob_repeat_allocate or
+ support_blob_repeat_allocate_shared. */
void support_blob_repeat_free (struct support_blob_repeat *);
#endif /* SUPPORT_BLOB_REPEAT_H */
diff --git a/support/tst-support_blob_repeat.c b/support/tst-support_blob_repeat.c
index a0eb9d2b89..b61d6b249a 100644
--- a/support/tst-support_blob_repeat.c
+++ b/support/tst-support_blob_repeat.c
@@ -17,6 +17,7 @@
<https://www.gnu.org/licenses/>. */
#include <stdio.h>
+#include <string.h>
#include <support/blob_repeat.h>
#include <support/check.h>
@@ -63,21 +64,39 @@ do_test (void)
}
support_blob_repeat_free (&repeat);
- repeat = support_blob_repeat_allocate ("012345678", 9, 10 * 1000 * 1000);
- if (repeat.start == NULL)
- puts ("warning: not enough memory for large mapping");
- else
+ for (int do_shared = 0; do_shared < 2; ++do_shared)
{
- unsigned char *p = repeat.start;
- for (int i = 0; i < 10 * 1000 * 1000; ++i)
- for (int j = 0; j <= 8; ++j)
- if (p[i * 9 + j] != '0' + j)
- {
- printf ("error: element %d index %d\n", i, j);
- TEST_COMPARE (p[i * 9 + j], '0' + j);
- }
+ if (do_shared)
+ repeat = support_blob_repeat_allocate_shared ("012345678", 9,
+ 10 * 1000 * 1000);
+ else
+ repeat = support_blob_repeat_allocate ("012345678", 9,
+ 10 * 1000 * 1000);
+ if (repeat.start == NULL)
+ puts ("warning: not enough memory for large mapping");
+ else
+ {
+ unsigned char *p = repeat.start;
+ for (int i = 0; i < 10 * 1000 * 1000; ++i)
+ for (int j = 0; j <= 8; ++j)
+ if (p[i * 9 + j] != '0' + j)
+ {
+ printf ("error: element %d index %d\n", i, j);
+ TEST_COMPARE (p[i * 9 + j], '0' + j);
+ }
+
+ enum { total_size = 9 * 10 * 1000 * 1000 };
+ p[total_size - 1] = '\0';
+ asm ("" ::: "memory");
+ if (do_shared)
+ /* The write is repeated in multiple places earlier in the
+ string due to page sharing. */
+ TEST_VERIFY (strlen (repeat.start) < total_size - 1);
+ else
+ TEST_COMPARE (strlen (repeat.start), total_size - 1);
+ }
+ support_blob_repeat_free (&repeat);
}
- support_blob_repeat_free (&repeat);
return 0;
}
next reply other threads:[~2020-05-05 13:55 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-05 13:55 Florian Weimer [this message]
2020-05-12 3:39 ` Carlos O'Donell
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