Makes sense to.
ok kettenis@
> On 06/30/2022 4:05 PM Martin Pieuchot <m...@openbsd.org> wrote:
>
>
> Diff below uses two tricks to make uvm_pagermapin/out() faster and less
> likely to fail in OOM situations.
>
> These functions are used to map buffers when swapping pages in/out and
> when faulting on mmaped files. robert@ even measured a 75% improvement
> when populating pages related to files that aren't yet in the buffer
> cache.
>
> The first trick is to use the direct map when available. I'm doing this
> for single pages but km_alloc(9) also does that for single segment...
> uvm_io() only maps one page at a time for the moment so this should be
> enough.
>
> The second trick is to use pmap_kenter_pa() which doesn't fail and is
> faster.
>
> With this changes the "freeze" happening on my server when entering many
> pages to swap in OOM situation is much shorter and the machine becomes
> quickly responsive.
>
> ok?
>
> Index: uvm/uvm_pager.c
> ===================================================================
> RCS file: /cvs/src/sys/uvm/uvm_pager.c,v
> retrieving revision 1.81
> diff -u -p -r1.81 uvm_pager.c
> --- uvm/uvm_pager.c 28 Jun 2022 19:07:40 -0000 1.81
> +++ uvm/uvm_pager.c 30 Jun 2022 13:34:46 -0000
> @@ -258,6 +258,16 @@ uvm_pagermapin(struct vm_page **pps, int
> vsize_t size;
> struct vm_page *pp;
>
> +#ifdef __HAVE_PMAP_DIRECT
> + /* use direct mappings for single page */
> + if (npages == 1) {
> + KASSERT(pps[0]);
> + KASSERT(pps[0]->pg_flags & PG_BUSY);
> + kva = pmap_map_direct(pps[0]);
> + return kva;
> + }
> +#endif
> +
> prot = PROT_READ;
> if (flags & UVMPAGER_MAPIN_READ)
> prot |= PROT_WRITE;
> @@ -273,14 +283,7 @@ uvm_pagermapin(struct vm_page **pps, int
> pp = *pps++;
> KASSERT(pp);
> KASSERT(pp->pg_flags & PG_BUSY);
> - /* Allow pmap_enter to fail. */
> - if (pmap_enter(pmap_kernel(), cva, VM_PAGE_TO_PHYS(pp),
> - prot, PMAP_WIRED | PMAP_CANFAIL | prot) != 0) {
> - pmap_remove(pmap_kernel(), kva, cva);
> - pmap_update(pmap_kernel());
> - uvm_pseg_release(kva);
> - return 0;
> - }
> + pmap_kenter_pa(cva, VM_PAGE_TO_PHYS(pp), prot);
> }
> pmap_update(pmap_kernel());
> return kva;
> @@ -294,8 +297,15 @@ uvm_pagermapin(struct vm_page **pps, int
> void
> uvm_pagermapout(vaddr_t kva, int npages)
> {
> +#ifdef __HAVE_PMAP_DIRECT
> + /* use direct mappings for single page */
> + if (npages == 1) {
> + pmap_unmap_direct(kva);
> + return;
> + }
> +#endif
>
> - pmap_remove(pmap_kernel(), kva, kva + ((vsize_t)npages << PAGE_SHIFT));
> + pmap_kremove(kva, (vsize_t)npages << PAGE_SHIFT);
> pmap_update(pmap_kernel());
> uvm_pseg_release(kva);
