I'd like to commit this soon unless there are objections.
Stefan Kempf wrote:
> The recent uvm commits fixed hangs because machines went out of memory
> because of using too much space for amap slots.
>
> It's possible to shrink memory requirements for amaps even more,
> but the current code needs some simplifications first. So here's another
> cleanup diff. There'll be one or two more before we get to the real stuff.
>
> This one simplifies the traversal of an amap when swap is disabled.
>
> There's no need to insert marker elements to find the next item in the
> amap list. The next amap can be determined by looking at the
> currently examined amap.
>
> Care must be taken to get the next element before the current amap is
> possibly deleted, and after all the current amap's pages were read in
> from swap (because the page-in may sleep and remove items from the amap
> list).
>
> ok?
>
> Index: uvm/uvm_amap.c
> ===
> RCS file: /cvs/src/sys/uvm/uvm_amap.c,v
> retrieving revision 1.62
> diff -u -p -r1.62 uvm_amap.c
> --- uvm/uvm_amap.c16 Mar 2016 16:53:43 - 1.62
> +++ uvm/uvm_amap.c17 Mar 2016 18:08:29 -
> @@ -902,21 +902,11 @@ amap_swap_off(int startslot, int endslot
> {
> struct vm_amap *am;
> struct vm_amap *am_next;
> - struct vm_amap marker_prev;
> - struct vm_amap marker_next;
> boolean_t rv = FALSE;
>
> -#if defined(DIAGNOSTIC)
> - memset(_prev, 0, sizeof(marker_prev));
> - memset(_next, 0, sizeof(marker_next));
> -#endif /* defined(DIAGNOSTIC) */
> -
> for (am = LIST_FIRST(_list); am != NULL && !rv; am = am_next) {
> int i;
>
> - LIST_INSERT_BEFORE(am, _prev, am_list);
> - LIST_INSERT_AFTER(am, _next, am_list);
> -
> for (i = 0; i < am->am_nused; i++) {
> int slot;
> int swslot;
> @@ -935,23 +925,14 @@ amap_swap_off(int startslot, int endslot
> rv = uvm_anon_pagein(anon);
>
> am->am_flags &= ~AMAP_SWAPOFF;
> - if (amap_refs(am) == 0) {
> - amap_wipeout(am);
> - am = NULL;
> + if (rv || amap_refs(am) == 0)
> break;
> - }
> - if (rv) {
> - break;
> - }
> i = 0;
> }
>
> - KASSERT(LIST_NEXT(_prev, am_list) == _next ||
> - LIST_NEXT(LIST_NEXT(_prev, am_list), am_list) ==
> - _next);
> - am_next = LIST_NEXT(_next, am_list);
> - LIST_REMOVE(_prev, am_list);
> - LIST_REMOVE(_next, am_list);
> + am_next = LIST_NEXT(am, am_list);
> + if (amap_refs(am) == 0)
> + amap_wipeout(am);
> }
>
> return rv;
