From mboxrd@z Thu Jan 1 00:00:00 1970 From: Neil Brown Date: Tue, 12 Aug 2008 16:23:08 +1000 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Message-ID: <18593.11340.609526.649904@notabene.brown> Subject: Re: [PATCH 12/30] mm: memory reserve management In-Reply-To: message from Peter Zijlstra on Thursday July 24 References: <20080724140042.408642539@chello.nl> <20080724141530.127530749@chello.nl> Sender: owner-linux-mm@kvack.org Return-Path: To: Peter Zijlstra Cc: Linus Torvalds , Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org, netdev@vger.kernel.org, trond.myklebust@fys.uio.no, Daniel Lezcano , Pekka Enberg List-ID: On Thursday July 24, a.p.zijlstra@chello.nl wrote: > Generic reserve management code. > > It provides methods to reserve and charge. Upon this, generic alloc/free style > reserve pools could be build, which could fully replace mempool_t > functionality. This looks quite different to last time I looked at the code (I think). You now have a more structured "kmalloc_reserve" interface which returns a flag to say if the allocation was from an emergency pool. I think this will be a distinct improvement at the call sites, though I haven't looked at them yet. :-) > + > +struct mem_reserve { > + struct mem_reserve *parent; > + struct list_head children; > + struct list_head siblings; > + > + const char *name; > + > + long pages; > + long limit; > + long usage; > + spinlock_t lock; /* protects limit and usage */ ^^^^^ > + > + wait_queue_head_t waitqueue; > +}; .... > +static void __calc_reserve(struct mem_reserve *res, long pages, long limit) > +{ > + unsigned long flags; > + > + for ( ; res; res = res->parent) { > + res->pages += pages; > + > + if (limit) { > + spin_lock_irqsave(&res->lock, flags); > + res->limit += limit; > + spin_unlock_irqrestore(&res->lock, flags); > + } > + } > +} I cannot figure out why the spinlock is being used to protect updates to 'limit'. As far as I can see, mem_reserve_mutex already protects all those updates. Certainly we need the spinlock for usage, but why for limit?? > + > +void *___kmalloc_reserve(size_t size, gfp_t flags, int node, void *ip, > + struct mem_reserve *res, int *emerg) > +{ .... > + if (emerg) > + *emerg |= 1; Why not just if (emerg) *emerg = 1. I can't we where '*emerg' can have any value but 0 or 1, so the '|' is pointless ??? Thanks, NeilBrown -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org