lkml.org 
[lkml]   [2008]   [May]   [5]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 05/10] Introduce ridr_get_new_above()
Tim Pepper wrote:
> On Tue 29 Apr at 16:33:09 +0200 Nadia.Derbey@bull.net said:
>
>>[PATCH 05/10]
>>
>>This patch introduces the ridr_get_new_above() routine, and some common code
>>between the idr an ridr API's.
>
>
> The ridr_get_new_above() is the first place we see something really
> different compared to idr (an RCU addition). This is a lot of patching
> so far for what would be a small incremental change otherwise.
>
>
>>Index: linux-2.6.25-mm1/include/linux/idr.h
>>===================================================================
>>--- linux-2.6.25-mm1.orig/include/linux/idr.h 2008-04-29 13:08:00.000000000 +0200
>>+++ linux-2.6.25-mm1/include/linux/idr.h 2008-04-29 14:08:47.000000000 +0200
>>@@ -71,6 +71,27 @@ struct idr {
>> }
>> #define DEFINE_IDR(name) struct idr name = IDR_INIT(name)
>>
>>+/* Actions to be taken after a call to _idr_sub_alloc */
>>+#define IDR_DONE -1
>>+#define IDR_NEED_TO_GROW -2
>>+#define IDR_NOMORE_SPACE -3
>>+#define IDR_GO_TOP -4
>>+#define IDR_GO_UP -5
>
>
> This stuff is useful on its own in as much as it improves code
> readability. A lot of this patch (the "some common code between the
> idr and ridr API's" part) could be a standalone patch distinct from the
> ridr series and then be at the head of your stack.
>
>
>>+ return action;
>>+ case IDR_DONE:
>>+ goto end_loop;
>>+ case IDR_GO_UP:
>>+ continue;
>>+ case IDR_GO_TOP:
>>+ goto restart;
>>+ default:
>>+ m = action;
>> break;
>>+ }
>>+ BUG_ON(m < 0);
>
>
> Why the added BUG_ON()? These couple hunks are a bit muddled, so maybe I
> missed something. But I don't see anything different in how m or bm are
> being manipulated such that m<0 is anymore likely after this patch.
>
>
>>Index: linux-2.6.25-mm1/lib/ridr.c
>>===================================================================
>>--- linux-2.6.25-mm1.orig/lib/ridr.c 2008-04-29 13:23:17.000000000 +0200
>>+++ linux-2.6.25-mm1/lib/ridr.c 2008-04-29 14:03:35.000000000 +0200
>>@@ -11,6 +11,23 @@
>> static struct kmem_cache *ridr_layer_cache;
>>
>>
>>+static struct ridr_layer *get_from_free_list(struct ridr *idp)
>>+{
>>+ struct ridr_layer *q;
>>+ struct idr_layer *p;
>>+ unsigned long flags;
>>+
>>+ spin_lock_irqsave(&idp->lock, flags);
>>+ if ((q = idp->id_free)) {
>>+ p = ridr_to_idr(q);
>>+ idp->id_free = p->ary[0];
>>+ idp->id_free_cnt--;
>>+ p->ary[0] = NULL;
>>+ }
>>+ spin_unlock_irqrestore(&idp->lock, flags);
>>+ return(q);
>>+}
>>+
>
>
> idr's alloc_layer() in disguise?
>
>
>>+static int sub_alloc(struct ridr *idp, int *starting_id,
>>+ struct ridr_layer **rpa, struct idr_layer **pa)
>
>
> ...
> More or less duplication
> ...
>
>
>>+ * Create the layer below if it is missing.
>>+ */
>>+ if (!p->ary[m]) {
>>+ new = get_from_free_list(idp);
>>+ if (!new)
>>+ return -1;
>>+ rcu_assign_pointer(p->ary[m], new);
>>+ p->count++;
>>+ }
>>+ pa[l] = p;
>>+ rpa[l--] = idr_to_ridr(p);
>>+ p = p->ary[m];
>>+ }
>>+
>>+end_loop:
>>+ pa[l] = p;
>>+ rpa[l] = idr_to_ridr(p);
>>+ return id;
>>+}
>
>
> Oh but wait..there's some RCU-ness tucked in there.
>
>
>>+
>>+static int ridr_get_empty_slot(struct ridr *idp, int starting_id,
>>+ struct ridr_layer **rpa, struct idr_layer **pa)
>>+{
>>+ struct ridr_layer *p, *rnew;
>>+ int layers, v, id;
>>+ unsigned long flags;
>>+
>>+ id = starting_id;
>>+build_up:
>>+ p = idp->top;
>>+ layers = idp->layers;
>>+ if (unlikely(!p)) {
>>+ p = get_from_free_list(idp);
>>+ if (!p)
>>+ return -1;
>>+ layers = 1;
>>+ }
>>+ /*
>>+ * Add a new layer to the top of the tree if the requested
>>+ * id is larger than the currently allocated space.
>>+ */
>>+ while (layers < MAX_LEVEL - 1 && id >= (1 << (layers * IDR_BITS))) {
>
> ^^ ^^
> Dropped some parens. Otherwise more duplication...
>
>
>>+ rnew->idr.ary[0] = NULL;
>>+ rnew->idr.bitmap = rnew->idr.count = 0;
>>+ __move_to_free_list(idp, rnew);
>>+ }
>>+ spin_unlock_irqrestore(&idp->lock, flags);
>>+ return -1;
>>+ }
>>+ _idr_set_new_slot(ridr_to_idr(rnew), ridr_to_idr(p));
>>+ p = rnew;
>>+ }
>>+ rcu_assign_pointer(idp->top, p);
>>+ idp->layers = layers;
>>+ v = sub_alloc(idp, &id, rpa, pa);
>>+ if (v == IDR_NEED_TO_GROW)
>>+ goto build_up;
>>+ return(v);
>>+}
>
>
> Some more RCU.
>
>
>>+static int ridr_get_new_above_int(struct ridr *idp, void *ptr, int starting_id)
>>+{
>>+ struct ridr_layer *rpa[MAX_LEVEL];
>>+ struct idr_layer *pa[MAX_LEVEL];
>>+ int id;
>>+
>>+ id = ridr_get_empty_slot(idp, starting_id, rpa, pa);
>>+ if (id >= 0) {
>>+ /*
>>+ * Successfully found an empty slot. Install the user
>>+ * pointer and mark the slot full.
>>+ */
>>+ rcu_assign_pointer(pa[0]->ary[id & IDR_MASK],
>>+ (struct ridr_layer *)ptr);
>>+ pa[0]->count++;
>>+ _idr_mark_full(pa, id);
>>+ }
>>+
>>+ return id;
>>+}
>
>
> And other line of RCU.
>
> OK. So at this point in patch 5/10 we've got 3 lines of new code and
> hundreds of lines of duplicated code?
>
> A while more looking through the rest of the patches for the rest of the
> context and I might be able to actually think about the implications of
> these three lines being where they are.
>
> Locking changes are complicated enough without all this obfuscation!
> I understand the desire to not break IDR, but...
>

OK, you convinced me. I'll re-send a new patchset that is incremental on
top of idr. Sorry (and thanks a lot) for the painful review!

Regards,
Nadia


\
 
 \ /
  Last update: 2008-05-05 12:37    [W:0.105 / U:1.484 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site