Re: [RFC PATCH 1/5] mm: intorduce __GFP_UNMAPPED and unmapped_alloc()

[Kent Overstreet]

On Thu, May 18, 2023 at 12:03:03PM -0700, Song Liu wrote:
> > Second, bitmap based solution cannot handle > 2MiB allocation cleanly,
> > while tree based solution can. For example, if a big driver uses 3MiB, the
> > tree based allocator can allocate 4MiB for it, and use the rest 1MiB for
> > smaller allocations.

2 MB is just a good default size for the initial unmapped allocations if
the main consideration is avoiding mapping fragmentation. The approach
can work with larger allocations if required.