Messages in this thread | | | From | Chris Wilson <> | Subject | Re: [RFC] Rebasing the IDR | Date | Mon, 11 Dec 2017 10:54:51 +0000 |
| |
Quoting Matthew Wilcox (2017-11-30 17:36:30) > About 40 of the approximately 180 users of the IDR in the kernel are > "1-based" instead of "0-based". That is, they never want to have ID 0 > allocated; they want to see IDs allocated between 1 and N. Usually, that's > expressed like this: > > /* Get the user-visible handle using idr. */ > ret = idr_alloc(&file_priv->object_idr, obj, 1, 0, GFP_KERNEL); > > The current implementation of this grieves me. You see, we mark each > node of the radix tree according to whether it has any free entries > or not, and entry 0 is always free! If we've already allocated 10,000 > entries from this IDR, and see this call, we'll walk all the way down > the left side of the tree looking for entry 1, get to the bottom, > see that entries 1-63 are allocated, then walk up to the next level, > see that 64-4095 are allocated, walk up to the next level, see that > 8192-12287 has a free entry, and then start walking down again.
Hmm, missing the baseline to apply this patch. But I did the quick hack of allocating index 0 of the idr and that did eradicate the idr_get_free_cmn() from being at the top of the profiles for the many-object stress tests. This improvement will be much appreciated. -Chris
| |