microsoft
Pickup page size from unistd.h
This uses the PAGESIZE constant from the unistd.h on POSIX. This should make the code more resilient to being compiled on platforms with different page sizes.
Sorry for the noise. git seems to have strange behaviour when checking out pr/head so my local change was not overwritten, which makes me think the issue was fixed.
The fix is not working. Such macro is undefined on platforms without a fixed page size.
#ifdef PAGESIZE
#warning "defined"
static constexpr size_t page_size = max(Aal::smallest_page_size, PAGESIZE);
#else
#warning "undefined"
static constexpr size_t page_size = Aal::smallest_page_size;
#endif
Gives undefined.
Actually, the corresponding header says
/* We do not provide fixed values for
ARG_MAX Maximum length of argument to the `exec' function
including environment data.
ATEXIT_MAX Maximum number of functions that may be registered
with `atexit'.
CHILD_MAX Maximum number of simultaneous processes per real
user ID.
OPEN_MAX Maximum number of files that one process can have open
at anyone time.
PAGESIZE
PAGE_SIZE Size of bytes of a page.
PASS_MAX Maximum number of significant bytes in a password.
We only provide a fixed limit for
IOV_MAX Maximum number of `iovec' structures that one process has
available for use with `readv' or writev'.
if this is indeed fixed by the underlying system.
*/
If this is not the on the perf-critical path, I suggest use _SC_PAGESIZE approach instead. It is the most portable way. In libc on linux, this value is usually populated via aux vector and cached by libc. There is no syscall involved. If you are concern that sysconf has a super large jumptable, you can also cache it inside snmalloc.
Inspected the code a little, it seems that a dynamic page size demands too many changes and may impact negatively on the performance. Is it possible to allow cmake to run sysconf or let user override page size during configuration phase? All these can be set as additional options.
Inspected the code a little, it seems that a dynamic page size demands too many changes and may impact negatively on the performance. Is it possible to allow
cmaketo runsysconfor let user override page size during configuration phase? All these can be set as additional options.
I would prefer the second. The first might have issues with cross compiling, so I wouldn't want to always run sysconf at configure time.
I think we could make the dynamic page size work, but it is more effort than I have time for, and would be pretty subtle to review the changes.