thanks Roland
I really don't like #if's on os's/systems
but I can't think of a way to reliably iffe overcommittment
I put in a change that assumes innocence until proven guilty
#if __linux__
/* check for mem overcommit */
#else
#endif
right now I only know of linux
do you know any others?
On Thu, 26 Apr 2012 01:38:08 +0200 Roland Mainz wrote:
> [AFAIK this is an old issue which somehow reappeared...]
> A while ago we found that libast's allocator creates a SIGSEGV handler
> for each chunk of memory obtained from the system to protect itself
> against getting wallpoed with a SIGSEGV if first tries to use a newly
> obtained memory page in cases when the kernel no longer has any
> physical memory left to actually map the page, e.g.
> like this:
> -- snip --
> mmap(0x00000000, 65536, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANON,
> -1, 0) = 0xFFFFFFFF53800000
> sigaction(SIGSEGV, 0xFFFFFFFF7FFFE320, 0xFFFFFFFF7FFFE428) = 0
> <newly obtained memory page is accessed here. If memory is not
> available the system will wallop the process with a SIGSEGV>
> sigaction(SIGSEGV, 0xFFFFFFFF7FFFE320, 0xFFFFFFFF7FFFE428) = 0
> -- snip --
> This makes sense if an operating system allows such overcommitment of
> memory but it doesn't make much sense if the OS doesn't allow this...
> like in Solaris case (maybe AIX, too...).
> The fix was to #ifdef-out the handler for Solaris but it seems the
> wrong cpp symbol was used, e.g. |_SUNOS| instead of |__SunOS|.
> The following patch will fix this issue:
> -- snip --
> diff --git a/src/lib/libast/vmalloc/vmbest.c b/src/lib/libast/vmalloc/vmbest.c
> index c291409..ff75b0a 100644
> --- a/src/lib/libast/vmalloc/vmbest.c
> +++ b/src/lib/libast/vmalloc/vmbest.c
> @@ -1111,7 +1111,7 @@ done:
> #endif
> #endif
> -#if _SUNOS /* sunos guarantees that brk-addresses are valid */
> +#if __SunOS /* sunos guarantees that brk-addresses are valid */
> #define chkaddr(a,n) (0)
> #else /* make sure that allocated memory are addressable */
> @@ -1140,7 +1140,7 @@ static int chkaddr(Vmuchar_t* addr, size_t nsize)
> return rv;
> }
> -#endif /*_SUNOS*/
> +#endif /*__SunOS*/
> #if _mem_win32 /
> -- snip --
> ----
> Bye,
> Roland
> --
> __ . . __
> (o.\ \/ /.o) [email protected]
> \__\/\/__/ MPEG specialist, C&&JAVA&&Sun&&Unix programmer
> /O /==\ O\ TEL +49 641 3992797
> (;O/ \/ \O;)
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