On Mon, 23 Apr 2007, Hisashi Hifumi wrote: > >No. The PG_lru flag bit is just one bit amongst many others: > >what of concurrent operations changing other bits in that same > >unsigned long e.g. trying to lock the page by setting PG_locked? > >There are some places where such micro-optimizations can be made > >(typically while first allocating the page); but in general, no. > > In i386 and x86_64, btsl is used to change page flag. In this case, if btsl > without lock prefix > set PG_locked and PG_lru flag concurrently, does only one operation > succeed ?
That's right: on an SMP machine, without the lock prefix, the operation is no longer atomic: what's stored back may be missing the result of one or the other of the racing operations. Hugh - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/