[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCHv2] frontswap: allow multiple backends
On Mon, 1 Jun 2015 10:22:24 -0400 Dan Streetman <ddstreet@xxxxxxxx> wrote: > Change frontswap single pointer to a singly linked list of frontswap > implementations. Update Xen tmem implementation as register no longer > returns anything. > > Frontswap only keeps track of a single implementation; any implementation > that registers second (or later) will replace the previously registered > implementation, and gets a pointer to the previous implementation that > the new implementation is expected to pass all frontswap functions to > if it can't handle the function itself. However that method doesn't > really make much sense, as passing that work on to every implementation > adds unnecessary work to implementations; instead, frontswap should > simply keep a list of all registered implementations and try each > implementation for any function. Most importantly, neither of the > two currently existing frontswap implementations in the kernel actually > do anything with any previous frontswap implementation that they > replace when registering. > > This allows frontswap to successfully manage multiple implementations > by keeping a list of them all. > > ... > > -struct frontswap_ops *frontswap_register_ops(struct frontswap_ops *ops) > +void frontswap_register_ops(struct frontswap_ops *ops) > { > - struct frontswap_ops *old = frontswap_ops; > - int i; > - > - for (i = 0; i < MAX_SWAPFILES; i++) { > - if (test_and_clear_bit(i, need_init)) { > - struct swap_info_struct *sis = swap_info[i]; > - /* __frontswap_init _should_ have set it! */ > - if (!sis->frontswap_map) > - return ERR_PTR(-EINVAL); > - ops->init(i); > - } > + DECLARE_BITMAP(a, MAX_SWAPFILES); > + DECLARE_BITMAP(b, MAX_SWAPFILES); > + struct swap_info_struct *si; > + unsigned int i; > + > + spin_lock(&swap_lock); > + plist_for_each_entry(si, &swap_active_head, list) { > + if (!WARN_ON(!si->frontswap_map)) > + set_bit(si->type, a); umm, DECLARE_BITMAP() doesn't initialise the storage. Either this patch wasn't tested very well or you should buy me a lottery ticket! > } > - /* > - * We MUST have frontswap_ops set _after_ the frontswap_init's > - * have been called. Otherwise __frontswap_store might fail. Hence > - * the barrier to make sure compiler does not re-order us. > + spin_unlock(&swap_lock); > + > + /* the new ops needs to know the currently active swap devices */ > + for_each_set_bit(i, a, MAX_SWAPFILES) > + ops->init(i); > + > + /* setting frontswap_ops must happen after the ops->init() calls > + * above; cmpxchg implies smp_mb() which will ensure the init is > + * complete at this point > + */ Like this, please: /* * Setting ... and sentences start with capital letters ;) _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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