Right, but you know from the first loop which order is applicable (and will be
fed to the second loop) and could just pte_unmap(pte) + tryalloc. If that fails,
remap and try with the next orders.
You mean something like this?
pte = pte_offset_map(vmf->pmd, vmf->address & PMD_MASK);
if (!pte)
return ERR_PTR(-EAGAIN);
order = highest_order(orders);
while (orders) {
addr = ALIGN_DOWN(vmf->address, PAGE_SIZE << order);
if (!pte_range_none(pte + pte_index(addr), 1 << order)) {
order = next_order(&orders, order);
continue;
}
pte_unmap(pte);
folio = vma_alloc_folio(gfp, order, vma, addr, true);
if (folio) {
clear_huge_page(&folio->page, vmf->address, 1 << order);
return folio;
}
pte = pte_offset_map(vmf->pmd, vmf->address & PMD_MASK);
if (!pte)
return ERR_PTR(-EAGAIN);
order = next_order(&orders, order);
}
pte_unmap(pte);
I don't really like that because if high order folio allocations fail, then you
are calling pte_range_none() again for the next lower order; once that check has
succeeded for an order it shouldn't be required for any lower orders. In this
case you also have lots of pte map/unmap.
I see what you mean.
The original version feels more efficient to me.
Yes it is. Adding in some comments might help, like
/*
* Find the largest order where the aligned range is completely prot_none(). Note
* that all remaining orders will be completely prot_none().
*/
...
/* Try allocating the largest of the remaining orders. */
That would make the code certainly easier to understand. That "orders" magic of
constructing, filtering, walking is confusing :)
I might find some time today to see if there is an easy way to cleanup all what
I spelled out above. It really is a mess. But likely that cleanup could be
deferred (but you're touching it, so ... :) ).
I'm going to ignore the last 5 words. I heard the "that cleanup could be
deferred" part loud and clear though :)
:)
If we could stop passing orders into thp_vma_allowable_orders(), that would probably
be the biggest win. It's just all a confusing mess.
--
Cheers,
David / dhildenb
