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Use mmap MAP_NOSYNC option to limit shared memory writes

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mmap() is rarely used for shared memory, but when it is, this option is
useful, particularly on the BSDs.

Patch by Sean Chittenden
This commit is contained in:
Bruce Momjian 2015-03-21 22:06:19 -04:00
parent 9d61b9953c
commit 34afbba84e
2 changed files with 10 additions and 2 deletions
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4
src/backend/storage/ipc/dsm_impl.c
View File

@ -368,7 +368,7 @@ dsm_impl_posix(dsm_op op, dsm_handle handle, Size request_size,
/* Map it. */
address = mmap(NULL, request_size, PROT_READ | PROT_WRITE,
MAP_SHARED | MAP_HASSEMAPHORE, fd, 0);
MAP_SHARED | MAP_HASSEMAPHORE | MAP_NOSYNC, fd, 0);
if (address == MAP_FAILED)
{
int save_errno;
@ -960,7 +960,7 @@ dsm_impl_mmap(dsm_op op, dsm_handle handle, Size request_size,
/* Map it. */
address = mmap(NULL, request_size, PROT_READ | PROT_WRITE,
MAP_SHARED | MAP_HASSEMAPHORE, fd, 0);
MAP_SHARED | MAP_HASSEMAPHORE | MAP_NOSYNC, fd, 0);
if (address == MAP_FAILED)
{
int save_errno;

8
src/include/portability/mem.h
View File

@ -30,6 +30,14 @@
#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. */