emaste updated this revision to Diff 6543.
emaste added a comment.
This revision now requires review to proceed.
- give full path to file with comment explaining the deadlock avoidance
- avoid confusing page mask manipulation and just touch the last byte explicitly
CHANGES SINCE LAST UPDATE
https://reviews.freebsd.org/D2933?vs=6524&id=6543
REVISION DETAIL
https://reviews.freebsd.org/D2933
AFFECTED FILES
usr.bin/ar/write.c
CHANGE DETAILS
diff --git a/usr.bin/ar/write.c b/usr.bin/ar/write.c
--- a/usr.bin/ar/write.c
+++ b/usr.bin/ar/write.c
@@ -41,6 +41,7 @@
#include <stdlib.h>
#include <string.h>
#include <sysexits.h>
+#include <unistd.h>
#include "ar.h"
@@ -61,6 +62,7 @@
static void free_obj(struct bsdar *bsdar, struct ar_obj *obj);
static void insert_obj(struct bsdar *bsdar, struct ar_obj *obj,
struct ar_obj *pos);
+static void prefault_buffer(const char *buf, size_t s);
static void read_objs(struct bsdar *bsdar, const char *archive,
int checkargv);
static void write_archive(struct bsdar *bsdar, char mode);
@@ -551,11 +553,35 @@
}
/*
+ * Fault in the buffer prior to writing as a workaround for poor performance
+ * due to interaction with kernel fs deadlock avoidance code. See the comment
+ * above vn_io_fault_doio() in sys/kern/vfs_vnops.c for details of the issue.
+ */
+static void
+prefault_buffer(const char *buf, size_t s)
+{
+ volatile const char *p;
+ size_t page_size;
+
+ if (s == 0)
+ return;
+ page_size = sysconf(_SC_PAGESIZE);
+ for (p = buf; p < buf + s; p += page_size)
+ *p;
+ /*
+ * Ensure we touch the last page as well, in case the buffer is not
+ * page-aligned.
+ */
+ *(volatile const char *)(buf + s - 1);
+}
+
+/*
* Wrapper for archive_write_data().
*/
static void
write_data(struct bsdar *bsdar, struct archive *a, const void *buf, size_t s)
{
+ prefault_buffer(buf, s);
if (archive_write_data(a, buf, s) != (ssize_t)s)
bsdar_errc(bsdar, EX_SOFTWARE, 0, "%s",
archive_error_string(a));
EMAIL PREFERENCES
https://reviews.freebsd.org/settings/panel/emailpreferences/
To: emaste, kib, eadler
Cc: kib, freebsd-toolchain-list, dim, davide
diff --git a/usr.bin/ar/write.c b/usr.bin/ar/write.c
--- a/usr.bin/ar/write.c
+++ b/usr.bin/ar/write.c
@@ -41,6 +41,7 @@
#include <stdlib.h>
#include <string.h>
#include <sysexits.h>
+#include <unistd.h>
#include "ar.h"
@@ -61,6 +62,7 @@
static void free_obj(struct bsdar *bsdar, struct ar_obj *obj);
static void insert_obj(struct bsdar *bsdar, struct ar_obj *obj,
struct ar_obj *pos);
+static void prefault_buffer(const char *buf, size_t s);
static void read_objs(struct bsdar *bsdar, const char *archive,
int checkargv);
static void write_archive(struct bsdar *bsdar, char mode);
@@ -551,11 +553,35 @@
}
/*
+ * Fault in the buffer prior to writing as a workaround for poor performance
+ * due to interaction with kernel fs deadlock avoidance code. See the comment
+ * above vn_io_fault_doio() in sys/kern/vfs_vnops.c for details of the issue.
+ */
+static void
+prefault_buffer(const char *buf, size_t s)
+{
+ volatile const char *p;
+ size_t page_size;
+
+ if (s == 0)
+ return;
+ page_size = sysconf(_SC_PAGESIZE);
+ for (p = buf; p < buf + s; p += page_size)
+ *p;
+ /*
+ * Ensure we touch the last page as well, in case the buffer is not
+ * page-aligned.
+ */
+ *(volatile const char *)(buf + s - 1);
+}
+
+/*
* Wrapper for archive_write_data().
*/
static void
write_data(struct bsdar *bsdar, struct archive *a, const void *buf, size_t s)
{
+ prefault_buffer(buf, s);
if (archive_write_data(a, buf, s) != (ssize_t)s)
bsdar_errc(bsdar, EX_SOFTWARE, 0, "%s",
archive_error_string(a));
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