Messages in this thread | | | Date | Fri, 14 May 2021 13:27:13 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH 26/94] Maple Tree: Add new data structure |
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On Fri, May 14, 2021 at 01:13:51PM +0200, Peter Zijlstra wrote: > On Wed, Apr 28, 2021 at 03:36:02PM +0000, Liam Howlett wrote:
> > +static inline struct maple_node *mte_to_node(const struct maple_enode *entry) > > +{ > > + return (struct maple_node *)((unsigned long)entry & ~127); > > +} > > > +static inline struct maple_topiary *mte_to_mat(const struct maple_enode *entry) > > +{ > > + return (struct maple_topiary *)((unsigned long)entry & ~127); > > +} > > Can we please write masks as hex, also do they want a pretty name? > > > This has more magic mask values, proper names might be good: > > > +static inline void mte_set_parent(struct maple_enode *enode, > > + const struct maple_enode *parent, > > + unsigned char slot) > > +{ > > + unsigned long bitmask = 0x78; > > + unsigned long val = (unsigned long) parent; > > + unsigned long type = 0; > > + > > + switch (mte_node_type(parent)) { > > + case maple_range_64: > > + case maple_arange_64: > > + type = 6; > > + break; > > + default: > > + break; > > + } > > + > > + val &= ~bitmask; // Remove any old slot number. > > + val |= (slot << MAPLE_PARENT_SHIFT); // Set the slot. > > + val |= type; > > + mte_to_node(enode)->parent = ma_parent_ptr(val); > > +} > > > +static inline unsigned int mte_parent_slot(const struct maple_enode *enode) > > +{ > > + unsigned long bitmask = 0x7C; > > + unsigned long val = (unsigned long) mte_to_node(enode)->parent; > > + > > + if (val & 1) > > + return 0; // Root. > > + > > + return (val & bitmask) >> MAPLE_PARENT_SHIFT; > > 7c is 1111100, but then you're shifting out the one bit that makes the > difference from the above magic 0x78. What gives?
IMO the more obvious way is something like:
(val >> MAPLE_PARENT_SHIFT) & ((1 << MAPLE_SLOT_BITS)-1);
And then we also see that 3+4 gives 7, which is that magical 127 above, are them the same? Related names would be good in that case.
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