On Sun, Feb 12, 2023 at 4:14 AM Andres Freund <and...@anarazel.de> wrote:
>
> > +ssize_t
> > +pg_pwrite_zeros(int fd, size_t size)
> > +{
> > + PGAlignedBlock zbuffer;
> > + size_t zbuffer_sz;
> > + struct iovec iov[PG_IOV_MAX];
> > + int blocks;
> > + size_t remaining_size = 0;
> > + int i;
> > + ssize_t written;
> > + ssize_t total_written = 0;
> > +
> > + zbuffer_sz = sizeof(zbuffer.data);
> > +
> > + /* Zero-fill the buffer. */
> > + memset(zbuffer.data, 0, zbuffer_sz);
>
> I previously commented on this - why are we memseting a buffer on every call
> to this? That's not at all free.
>
> Something like
> static const PGAlignedBlock zerobuf = {0};
> would do the trick. You do need to cast the const away, to assign to
> iov_base, but that's not too ugly.
Thanks for looking at it. We know that we don't change the zbuffer in
the function, so can we avoid static const and have just a static
variable, like the attached
v1-0001-Use-static-variable-to-avoid-memset-calls-in-pg_p.patch? Do
you see any problem with it?
FWIW, it comes out like the attached
v1-0001-Use-static-const-variable-to-avoid-memset-calls-i.patch with
static const.
--
Bharath Rupireddy
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com
From 2527c6083bbdf006900be1a1dbf15ed815184d2b Mon Sep 17 00:00:00 2001
From: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>
Date: Sun, 12 Feb 2023 10:58:33 +0000
Subject: [PATCH v1] Use static variable to avoid memset() calls in
pg_pwrite_zeros()
---
src/common/file_utils.c | 8 +++-----
1 file changed, 3 insertions(+), 5 deletions(-)
diff --git a/src/common/file_utils.c b/src/common/file_utils.c
index 4dae534152..0d59488f60 100644
--- a/src/common/file_utils.c
+++ b/src/common/file_utils.c
@@ -539,7 +539,8 @@ pg_pwritev_with_retry(int fd, const struct iovec *iov, int iovcnt, off_t offset)
ssize_t
pg_pwrite_zeros(int fd, size_t size)
{
- PGAlignedBlock zbuffer; /* worth BLCKSZ */
+ /* Zero-filled buffer worth BLCKSZ. */
+ static PGAlignedBlock zbuffer = {0};
size_t zbuffer_sz;
struct iovec iov[PG_IOV_MAX];
int blocks;
@@ -548,10 +549,7 @@ pg_pwrite_zeros(int fd, size_t size)
ssize_t written;
ssize_t total_written = 0;
- zbuffer_sz = sizeof(zbuffer.data);
-
- /* Zero-fill the buffer. */
- memset(zbuffer.data, 0, zbuffer_sz);
+ zbuffer_sz = BLCKSZ;
/* Prepare to write out a lot of copies of our zero buffer at once. */
for (i = 0; i < lengthof(iov); ++i)
--
2.34.1
From adc5ea83fb6726a5d8a1f3b87d6b3b03550c7fcb Mon Sep 17 00:00:00 2001
From: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>
Date: Sun, 12 Feb 2023 10:55:09 +0000
Subject: [PATCH v1] Use static const variable to avoid memset calls in
pg_pwrite_zeros
---
src/common/file_utils.c | 10 ++++------
1 file changed, 4 insertions(+), 6 deletions(-)
diff --git a/src/common/file_utils.c b/src/common/file_utils.c
index 4dae534152..cd15cc2fdb 100644
--- a/src/common/file_utils.c
+++ b/src/common/file_utils.c
@@ -539,7 +539,8 @@ pg_pwritev_with_retry(int fd, const struct iovec *iov, int iovcnt, off_t offset)
ssize_t
pg_pwrite_zeros(int fd, size_t size)
{
- PGAlignedBlock zbuffer; /* worth BLCKSZ */
+ /* Zero-filled buffer worth BLCKSZ. */
+ static const PGAlignedBlock zbuffer = {0};
size_t zbuffer_sz;
struct iovec iov[PG_IOV_MAX];
int blocks;
@@ -548,15 +549,12 @@ pg_pwrite_zeros(int fd, size_t size)
ssize_t written;
ssize_t total_written = 0;
- zbuffer_sz = sizeof(zbuffer.data);
-
- /* Zero-fill the buffer. */
- memset(zbuffer.data, 0, zbuffer_sz);
+ zbuffer_sz = BLCKSZ;
/* Prepare to write out a lot of copies of our zero buffer at once. */
for (i = 0; i < lengthof(iov); ++i)
{
- iov[i].iov_base = zbuffer.data;
+ iov[i].iov_base = (void *) (unconstify(PGAlignedBlock *, &zbuffer)->data);
iov[i].iov_len = zbuffer_sz;
}
--
2.34.1
