Messages in this thread | | | Date | Fri, 13 Dec 2019 11:50:42 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH 4/5] locking/lockdep: Reuse free chain_hlocks entries |
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On Fri, Dec 13, 2019 at 11:25:25AM +0100, Peter Zijlstra wrote:
> void push_block(struct chain_block **bp, struct chain_block *b) > { > b->next = *bp; > *bp = b; > } > > /* could contemplate ilog2() buckets */ > int size2bucket(int size) > { > return size >= MAX_BUCKET ? 0 : size; > }
If you make the allocation granularity 4 entries, then you can have push_block() store the chain_block * at the start of every free entry, which would enable merging adjecent blocks.
That is, if I'm not mistaken these u16 chain entries encode the class index (per lock_chain_get_class()). And since the lock_classes array is MAX_LOCKDEP_KEYS, or 13 bits, big, we have the MSB of each entry spare.
union { struct { u16 hlock[4]; } u64 addr; } ponies;
So if we make the rule that:
!(idx % 4) && (((union ponies *)chain_hlock[idx])->addr & BIT_ULL(63))
encodes a free block at said addr, then we should be able to detect if:
chain_hlock[b->base + b->size]
is also free and merge the blocks.
(we just have to fix up the MSB of the address, not all arches have negative addresses for kernel space)
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