> From: linux-rdma-owner@xxxxxxxxxxxxxxx <linux-rdma-
> owner@xxxxxxxxxxxxxxx> On Behalf Of Jason Gunthorpe
>
> > + xa_lock(&ucontext->mmap_xa);
> > + if (check_add_overflow(ucontext->mmap_xa_page,
> > + (u32)(length >> PAGE_SHIFT),
> > + &next_mmap_page))
> > + goto err_unlock;
>
> I still don't like that this algorithm latches into a permanent failure when the
> xa_page wraps.
>
> It seems worth spending a bit more time here to tidy this.. Keep using the
> mmap_xa_page scheme, but instead do something like
>
> alloc_cyclic_range():
>
> while () {
> // Find first empty element in a cyclic way
> xa_page_first = mmap_xa_page;
> xa_find(xa, &xa_page_first, U32_MAX, XA_FREE_MARK)
>
> // Is there a enough room to have the range?
> if (check_add_overflow(xa_page_first, npages, &xa_page_end)) {
> mmap_xa_page = 0;
> continue;
> }
>
> // See if the element before intersects
> elm = xa_find(xa, &zero, xa_page_end, 0);
> if (elm && intersects(xa_page_first, xa_page_last, elm->first, elm->last)) {
> mmap_xa_page = elm->last + 1;
> continue
> }
>
> // xa_page_first -> xa_page_end should now be free
> xa_insert(xa, xa_page_start, entry);
> mmap_xa_page = xa_page_end + 1;
> return xa_page_start;
> }
>
> Approximately, please check it.
Gal & Jason,
Coming back to the mmap_xa_page algorithm. I couldn't find some background on this.
Why do you need the length to be represented in the mmap_xa_page ?
Why not simply use xa_alloc_cyclic ( like in siw )
This is simply a key to a mmap object...
Thanks,
Michal
