Re: [Nbd] [PATCH] nbd-client: adjust the oom-killer score in swap mode

[Wouter Verhelst <w@...112...>]

On Fri, Jun 22, 2012 at 12:59:22AM +0400, Dmitry V. Levin wrote:
> In swap mode, it is highly desirable to take all available measures that
> could help nbd-client survival in low memory conditions.  One of such
> measures is to disable oom killing of nbd-client by adjusting the
> oom-killer score.

Make sense. But since nbd-client is linux-only, the #ifdef __linux__"
bits are redundant...

> Signed-off-by: Dmitry V. Levin <ldv@...1147...>
> ---
>  man/nbd-client.8.in.sgml |    5 +++--
>  nbd-client.c             |   26 ++++++++++++++++++++++++++
>  2 files changed, 29 insertions(+), 2 deletions(-)
> 
> diff --git a/man/nbd-client.8.in.sgml b/man/nbd-client.8.in.sgml
> index 4f24a61..8c862a1 100644
> --- a/man/nbd-client.8.in.sgml
> +++ b/man/nbd-client.8.in.sgml
> @@ -211,8 +211,9 @@ manpage.1: manpage.sgml
>  	<listitem>
>  	  <para>Specifies that this NBD device will be used as
>  	  swapspace. This option attempts to prevent deadlocks by
> -	  performing mlockall() at an appropriate time. It does not
> -	  however guarantee that such deadlocks can be avoided.</para>
> +	  performing mlockall() and adjusting the oom-killer score
> +	  at an appropriate time. It does not however guarantee
> +	  that such deadlocks can be avoided.</para>
>  	</listitem>
>        </varlistentry>
>        <varlistentry>
> diff --git a/nbd-client.c b/nbd-client.c
> index 2321e7b..5526db0 100644
> --- a/nbd-client.c
> +++ b/nbd-client.c
> @@ -372,6 +372,23 @@ void finish_sock(int sock, int nbd, int swap) {
>  		mlockall(MCL_CURRENT | MCL_FUTURE);
>  }
>  
> +#ifdef __linux__
> +static int
> +oom_adjust(const char *file, const char *value)
> +{
> +	int fd, rc;
> +	size_t len;
> +
> +	fd = open(file, O_WRONLY);
> +	if (fd < 0)
> +		return -1;
> +	len = strlen(value);
> +	rc = write(fd, value, len) != (ssize_t) len;
> +	close(fd);
> +	return rc ? -1 : 0;
> +}
> +#endif
> +
>  void usage(char* errmsg, ...) {
>  	if(errmsg) {
>  		char tmp[256];
> @@ -561,6 +578,15 @@ int main(int argc, char *argv[]) {
>  	setsizes(nbd, size64, blocksize, flags);
>  	set_timeout(nbd, timeout);
>  	finish_sock(sock, nbd, swap);
> +#ifdef __linux__
> +	if (swap) {
> +		/* try linux >= 2.6.36 interface first */
> +		if (oom_adjust("/proc/self/oom_score_adj", "-1000")) {
> +			/* fall back to linux <= 2.6.35 interface */
> +			oom_adjust("/proc/self/oom_adj", "-17");
> +		}
> +	}
> +#endif
>  
>  	/* Go daemon */
>  	
> -- 
> ldv
> 
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