On Wed, Oct 12, 2022 at 4:37 PM David Rowley <dgrowle...@gmail.com> wrote: > [v3]
+ /* + * Compute a shift that guarantees that shifting chunksPerBlock with it + * yields is smaller than SLAB_FREELIST_COUNT - 1 (one freelist is used for full blocks). + */ + slab->freelist_shift = 0; + while ((slab->chunksPerBlock >> slab->freelist_shift) >= (SLAB_FREELIST_COUNT - 1)) + slab->freelist_shift++; + /* + * Ensure, without a branch, that index 0 is only used for blocks entirely + * without free chunks. + * XXX: There probably is a cheaper way to do this. Needing to shift twice + * by slab->freelist_shift isn't great. + */ + index = (freecount + (1 << slab->freelist_shift) - 1) >> slab->freelist_shift; How about something like #define SLAB_FREELIST_COUNT ((1<<3) + 1) index = (freecount & (SLAB_FREELIST_COUNT - 2)) + (freecount != 0); and dispense with both freelist_shift and the loop that computes it? -- John Naylor EDB: http://www.enterprisedb.com
