On Mon, Oct 13, 2014 at 11:35:18AM -0400, Bruce Momjian wrote:
> On Mon, Oct 13, 2014 at 05:21:32PM +0200, Andres Freund wrote:
> > > If we have it, we should improve it, or remove it. We might want to use
> > > this code for something else in the future, so it should be improved
> > > where feasible.
> >
> > Meh. We don't put in effort into code that doesn't matter just because
> > it might get used elsewhere some day. By that argument we'd need to
> > performance optimize a lot of code. And actually, using that code
> > somewhere else is more of a counter indication than a pro
> > argument. MAP_NOSYNC isn't a general purpose flag.
>
> The key is that this is platform-specific behavior, so if we should use
> a flag to use it right, we should. You are right that optimizing
> rarely used code with generic calls isn't a good use of time.
I have adjusted Sean's mmap() options patch to match our C layout and
plan to apply this to head, as it is from August.
--
Bruce Momjian <br...@momjian.us> http://momjian.us
EnterpriseDB http://enterprisedb.com
+ Everyone has their own god. +
diff --git a/src/backend/storage/ipc/dsm_impl.c b/src/backend/storage/ipc/dsm_impl.c
new file mode 100644
index cf7938c..0859fbf
*** a/src/backend/storage/ipc/dsm_impl.c
--- b/src/backend/storage/ipc/dsm_impl.c
*************** dsm_impl_posix(dsm_op op, dsm_handle han
*** 368,374 ****
/* Map it. */
address = mmap(NULL, request_size, PROT_READ | PROT_WRITE,
! MAP_SHARED | MAP_HASSEMAPHORE, fd, 0);
if (address == MAP_FAILED)
{
int save_errno;
--- 368,374 ----
/* Map it. */
address = mmap(NULL, request_size, PROT_READ | PROT_WRITE,
! MAP_SHARED | MAP_HASSEMAPHORE | MAP_NOSYNC, fd, 0);
if (address == MAP_FAILED)
{
int save_errno;
*************** dsm_impl_mmap(dsm_op op, dsm_handle hand
*** 960,966 ****
/* Map it. */
address = mmap(NULL, request_size, PROT_READ | PROT_WRITE,
! MAP_SHARED | MAP_HASSEMAPHORE, fd, 0);
if (address == MAP_FAILED)
{
int save_errno;
--- 960,966 ----
/* Map it. */
address = mmap(NULL, request_size, PROT_READ | PROT_WRITE,
! MAP_SHARED | MAP_HASSEMAPHORE | MAP_NOSYNC, fd, 0);
if (address == MAP_FAILED)
{
int save_errno;
diff --git a/src/include/portability/mem.h b/src/include/portability/mem.h
new file mode 100644
index 7c77dbd..a4b01fe
*** a/src/include/portability/mem.h
--- b/src/include/portability/mem.h
***************
*** 30,35 ****
--- 30,43 ----
#define MAP_HASSEMAPHORE 0
#endif
+ /*
+ * BSD-derived systems use the MAP_NOSYNC flag to prevent dirty mmap(2)
+ * pages from being gratuitously flushed to disk.
+ */
+ #ifndef MAP_NOSYNC
+ #define MAP_NOSYNC 0
+ #endif
+
#define PG_MMAP_FLAGS (MAP_SHARED|MAP_ANONYMOUS|MAP_HASSEMAPHORE)
/* Some really old systems don't define MAP_FAILED. */
--
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