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But non-uni= form split >> only requires at most 1 xa_node allocation. For example, to split an o= rder-9 >> folio, 8 xa_nodes are needed for uniform split, since the folio takes = 8 >> multi-index slots in the xarray. But for non-uniform split, only the s= lot >> containing the given struct page needs a xa_node after the split. Ther= e will be >> a 7 xa_node saving. >> >> Hi Matthew, >> >> Do you mind checking my statement above on xarray memory saving? And c= orrect me >> if I miss anything. Thanks. > > We currently have a bug where we can't split order-12 (or above) to ord= er-0 (or anything in the range 0-5) as we'd need to allocate two layers o= f nodes, and > the preallocation can't do that. > > As part of your series, I'd like to remove that limitation, so we'd nee= d > to allocate log_64(n - m) [ok, more complex than that, but ykwim]. So > it's not quite "only allocate one node", but it's allocate O(log(curren= t > number of nodes needed to be allocated)). > > Makes sense? Yes. To remove that order-12 limitation, do shmem_split_large_entry() and __filemap_add_folio() need some change as well? Both call xas_split_alloc= (). But I do not know if they will see splitting order-12 to order-(0 to 5). Best Regards, Yan, Zi