vm_phys: reduce touching of page->pool fields

[dougm]

Summary

Change the usage of the pool field in vm_page structs.

Currently, every page belongs to a pool, and the pool field identifies that pool, whether the page is allocated or free.

With this change, the pool field of the first page of a free block is used by the buddy allocator to identify its pool, but the buddy allocator makes no guarantees about the pool field value for allocated pages. The buddy allocator requires that a pool parameter be passed as part of freeing memory. A function that allocates memory may use the pool field of a page to record what pool to pass as that parameter when the memory is freed, but might not need to do so for every allocated page.

Test Plan

Running buildworlds.

[dougm]

In response to offline feedback, reduce needless changes to the pool field, where it is changed from A to B and then back to A.

[dougm]

Break a too-long line.

[dougm]

Add a KASSERT.

[dougm]

In vm_phys_free_pages, I'd be happy to make a change that might not be strictly in the spirit of this change.

I note that m is not dereferenced in the inner do-while loop. It is only computed. So, if it weren't computed in the loop, then after the loop you could have

if (order < VM_NFREEORDER - 1)

pa ^= ((vm_paddr_t)1 << (PAGE_SHIFT + order));

m = &seg->first_page[...];

Then you could replace m_buddy with m.

[dougm]

Avoid an unneeded write to pool in phys_free_pages.

[dougm]

Drop an unneeded assignment to ->pool in _unfree().

[dougm]

Resolve conflicts that arise when ilog2 was introduced to vm_phys.c.

[dougm]

Update after FREEPOOL_LAZYINIT changes.

[dougm]

Remove a blank line.

[dougm]

Update to resolve a vm_reserv.c conflict.

[dougm]

The overall timing results of running a dozen or so make-worlds without (base) and with (pool) this change:

x base.time
+ pool.time
+------------------------------------------------------------------------------+
|+x ++  x+   +    +   x+   +* xx   + xx x  x    x  ++       +                 x|
|    |__________|______M_A_________A_M_______|_______|                         |
+------------------------------------------------------------------------------+
    N           Min           Max        Median           Avg        Stddev
x  13       3794.47       3828.59       3810.03     3809.0946     8.4516533
+  13       3794.02       3820.52       3804.11     3804.8223     8.8034663
No difference proven at 95.0% confidence

[dougm]

Remove a needless assignment to m->pool

[dougm]

Reran 13 buildworlds after one-line change; here are the results, compared to the same 13 buildworlds on unmodified kernel:

x base.time
+ pool.time
+------------------------------------------------------------------------------+
|                             +                                                |
|                             +            x        +                          |
|x     x             x++  +x +*x  + x x x  x  + x + +      +                  x|
|              |_________|____M___A_MA____________|__|                         |
+------------------------------------------------------------------------------+
    N           Min           Max        Median           Avg        Stddev
x  13       3794.47       3828.59       3810.03     3809.0946     8.4516533
+  13       3803.98       3820.27       3807.45     3810.5046      5.579744
No difference proven at 95.0% confidence

[dougm]

Let vm_phys_alloc_npages clear all pool values in allocated memory, with the function vm_phys_free_npages supplying the pool as a parameter.

[dougm]

Updated stats comparing base buildworld times with times after applying this patch:

x base.time
+ pool3.time
+------------------------------------------------------------------------------+
|                                 +                                            |
|                                 +                                            |
|+ +     x  x  x + x+ x+   x   x  +    * + x    *x+   x +                     x|
|             ||_______________A__M_____________|_____|                        |
+------------------------------------------------------------------------------+
    N           Min           Max        Median           Avg        Stddev
x  13       3799.46       3826.48       3807.97       3809.38     7.7810464
+  13       3796.29       3817.71       3809.23       3807.95     6.7123679
No difference proven at 95.0% confidence

[dougm]

base - unmodified, pool-with these changes

x base
+ pool
+------------------------------------------------------------------------------+
|                                          +         x                         |
|+            + +x *+        x  x  +*   x  +x    +*  x x x    +     +         x|
|              |__________|________AM______AM__________|____|                  |
+------------------------------------------------------------------------------+
    N           Min           Max        Median           Avg        Stddev
x  13       3800.14       3820.84       3809.25     3809.0408     5.7418775
+  13       3794.66       3817.48       3806.45     3806.2346     6.7908745
No difference proven at 95.0% confidence

[dougm]

No changes, just an update to account for some lines that just got renumbered.

[alc]

This is much better.

[dougm]

Refresh.