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Commit712704d

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Remove redundant ftruncate() for POSIX DSM memory.
In early releases of the DSM infrastructure, it was possible to resizesegments. That was removed in release 12 by commit3c60d0f. Now theftruncate() + posix_fallocate() sequence during DSM segment creation hasa redundant step: we're always extending from zero to the desired size,so we might as well just call posix_fallocate().Let's also include the remaining ftruncate() call (non-Linux POSIXsystems) in the wait event reporting, for good measure.Discussion:https://postgr.es/m/CA%2BhUKGJSm-nq8s%2B_59zb7NbFQF-OS%3DxTnTAiGLrQpuSmU2y_1A%40mail.gmail.com
1 parent4518c79 commit712704d

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+25
-29
lines changed

1 file changed

+25
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lines changed

‎src/backend/storage/ipc/dsm_impl.c

Lines changed: 25 additions & 29 deletions
Original file line numberDiff line numberDiff line change
@@ -364,43 +364,39 @@ dsm_impl_posix_resize(int fd, off_t size)
364364
*/
365365
PG_SETMASK(&BlockSig);
366366

367-
/* Truncate (or extend) the file to the requested size. */
368-
do
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{
370-
rc=ftruncate(fd,size);
371-
}while (rc<0&&errno==EINTR);
372-
367+
pgstat_report_wait_start(WAIT_EVENT_DSM_FILL_ZERO_WRITE);
368+
#if defined(HAVE_POSIX_FALLOCATE)&& defined(__linux__)
373369
/*
374-
* On Linux, a shm_open fd is backed by a tmpfs file.After resizing with
375-
* ftruncate, the filemay contain a hole. Accessing memory backed by a
370+
* On Linux, a shm_open fd is backed by a tmpfs file.If we were to use
371+
* ftruncate, the filewould contain a hole. Accessing memory backed by a
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* hole causes tmpfs to allocate pages, which fails with SIGBUS if there
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* is no more tmpfs space available. So we ask tmpfs to allocate pages
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* here, so we can fail gracefully with ENOSPC now rather than risking
379375
* SIGBUS later.
376+
*
377+
* We still use a traditional EINTR retry loop to handle SIGCONT.
378+
* posix_fallocate() doesn't restart automatically, and we don't want
379+
* this to fail if you attach a debugger.
380380
*/
381-
#if defined(HAVE_POSIX_FALLOCATE)&& defined(__linux__)
382-
if (rc==0)
381+
do
383382
{
384-
/*
385-
* We still use a traditional EINTR retry loop to handle SIGCONT.
386-
* posix_fallocate() doesn't restart automatically, and we don't want
387-
* this to fail if you attach a debugger.
388-
*/
389-
pgstat_report_wait_start(WAIT_EVENT_DSM_FILL_ZERO_WRITE);
390-
do
391-
{
392-
rc=posix_fallocate(fd,0,size);
393-
}while (rc==EINTR);
394-
pgstat_report_wait_end();
383+
rc=posix_fallocate(fd,0,size);
384+
}while (rc==EINTR);
395385

396-
/*
397-
* The caller expects errno to be set, but posix_fallocate() doesn't
398-
* set it. Instead it returns error numbers directly. So set errno,
399-
* even though we'll also return rc to indicate success or failure.
400-
*/
401-
errno=rc;
402-
}
403-
#endif/* HAVE_POSIX_FALLOCATE && __linux__ */
386+
/*
387+
* The caller expects errno to be set, but posix_fallocate() doesn't
388+
* set it. Instead it returns error numbers directly. So set errno,
389+
* even though we'll also return rc to indicate success or failure.
390+
*/
391+
errno=rc;
392+
#else
393+
/* Extend the file to the requested size. */
394+
do
395+
{
396+
rc=ftruncate(fd,size);
397+
}while (rc<0&&errno==EINTR);
398+
#endif
399+
pgstat_report_wait_end();
404400

405401
save_errno=errno;
406402
PG_SETMASK(&UnBlockSig);

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