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Differential D20579

Remove limit on blist_alloc maxsize, allow bigger getswapspace allocations
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Authored by dougm on Jun 9 2019, 7:19 PM.
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rS349777: Change blist_next_leaf_alloc so that it can examine more than one leaf
Summary

Change blist_next_leaf_alloc so that it can examine more than one leaf after the one where the possible block allocation begins, and allocate a larger number of blocks than the current limit. This does not affect the limit on minimum allocation size, which still cannot exceed BLIST_MAX_ALLOC.

Use this change to modify swp_pager_getswapspace and its callers, so that it can allocate more than BLIST_MAX_ALLOC blocks if they are available, to avoid a later call that would allocate those blocks anyway.

The change to blist_next_leaf_alloc could also be used to support TRIM, to grab a large number of blocks at a time to get trimmed. That would require other changes, including a new "trimming cursor" that stays ahead of the regular cursor, but none of that is implemented yet.

Test Plan

I can boot a kernel with this patch. I'm not sure how to test to guarantee that swp_pager_getswapspace calls with npages > BLIST_MAX_ALLOC will be exercised.

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Event Timeline

dougm created this revision.Jun 9 2019, 7:19 PM
markj added inline comments.Jun 21 2019, 8:14 PM
kern/subr_blist.c
621

As a matter of style I would prefer to avoid introducing new camel case names.

627–651

We are assuming that startBlk is 0 mod BLIST_BMAP_RADIX, is that right?

633

This line should be indented by four spaces.

637

I don't quite understand this. How are we sure that scan is a leaf node?

668–670

This line should be indented by four spaces.

vm/swap_pager.c
733

Should this be imin()?

1385–1386

Now that number is one. :)

dougm updated this revision to Diff 58876.Jun 21 2019, 10:19 PM
dougm marked 7 inline comments as done.

By renaming, re-indenting, and updating stale comments, seek to answer questions and address reviewer concerns.

markj added a comment.Jul 4 2019, 6:34 PM

I apologize for the delay in getting back to this.

I can boot a kernel with this patch. I'm not sure how to test to guarantee that swp_pager_getswapspace calls with npages > BLIST_MAX_ALLOC will be exercised.

You'd need to at least bump the value of vm_pageout_page_count.

kern/subr_blist.c
654

Here we're clearing bits from the next leaf. Isn't it possible that we are allocating blocks from multiple leaf nodes starting at start if maxcount is sufficiently large?

655

Why can't this be written as maxcount % BLIST_BMAP_RADIX?

vm/swap_pager.c
1386

"limited by"

dougm updated this revision to Diff 59404.Jul 4 2019, 6:56 PM
dougm marked 3 inline comments as done.

Add/alter comments and slightly restructure a computation in response to reviewer comments.

pho added a comment.Jul 5 2019, 11:20 AM

Typo?

cc -c -O2 -pipe -fno-strict-aliasing  -g -nostdinc  -I. -I../../.. -I../../../contrib/ck/include -I../../../contrib/libfdt -D_KERNEL -DHAVE_KERNEL_OPTION_HEADERS -include opt_global.h    -fno-omit-frame-pointer -mno-omit-leaf-frame-pointer -MD  -MF.depend.subr_blist.o -MTsubr_blist.o -fdebug-prefix-map=./machine=/usr/src/sys/amd64/include -fdebug-prefix-map=./x86=/usr/src/sys/x86/include -mcmodel=kernel -mno-red-zone -mno-mmx -mno-sse -msoft-float  -fno-asynchronous-unwind-tables -ffreestanding -fwrapv -fstack-protector -gdwarf-2 -Wall -Wredundant-decls -Wnested-externs -Wstrict-prototypes -Wmissing-prototypes -Wpointer-arith -Wcast-qual -Wundef -Wno-pointer-sign -D__printf__=__freebsd_kprintf__ -Wmissing-include-dirs -fdiagnostics-show-option -Wno-unknown-pragmas -Wno-error-tautological-compare -Wno-error-empty-body -Wno-error-parentheses-equality -Wno-error-unused-function -Wno-error-pointer-sign -Wno-error-shift-negative-value -Wno-address-of-packed-member  -mno-aes -mno-avx  -std=iso9899:1999 -Werror  ../../../kern/subr_blist.c                                                                                                                                                
../../../kern/subr_blist.c:659:17: error: use of undeclared identifier 'BLIST_MAP_RADIX'
        if (maxcount % BLIST_MAP_RADIX != 0)
                       ^
1 error generated.
*** Error code 1
dougm updated this revision to Diff 59444.Jul 5 2019, 3:09 PM

Fix typo.

markj accepted this revision.Jul 5 2019, 3:14 PM
This revision is now accepted and ready to land.Jul 5 2019, 3:14 PM
pho added a comment.Jul 5 2019, 8:15 PM

I have run tests on D20579.59404.diff (with the typo fixed) for 8 hours. This included a buildworld / installworld.

Closed by commit rS349777: Change blist_next_leaf_alloc so that it can examine more than one leaf (authored by dougm). · Explain WhyJul 6 2019, 6:15 AM
This revision was automatically updated to reflect the committed changes.
dougm added a commit: rS349777: Change blist_next_leaf_alloc so that it can examine more than one leaf.
Herald added a subscriber: imp. · View Herald TranscriptJul 6 2019, 6:15 AM
pho added a comment.Jul 9 2019, 10:24 AM

Looks like this patch is responsible for the panics I see.

20190709 11:56:55 all (1/1): sort.sh
swap_pager: out of swap space
swp_pager_getswapspace(32): failed
Jul  9 12:03:41 mercat1 kernel: pid 3581 (sort), jid 0, uid 0, was killed: out of swap space
Jul  9 12:03:42 mercat1 kernel: pid 3583 (sort), jid 0, uid 0, was killed: out of swap space
panic: freeing free block: ffffc0, size 16, mask 1
cpuid = 7
time = 1562666624
KDB: stack backtrace:
db_trace_self_wrapper() at db_trace_self_wrapper+0x2b/frame 0xfffffe102d95b270
vpanic() at vpanic+0x19d/frame 0xfffffe102d95b2c0
panic() at panic+0x43/frame 0xfffffe102d95b320
blst_meta_free() at blst_meta_free+0x12b/frame 0xfffffe102d95b360
blst_meta_free() at blst_meta_free+0x102/frame 0xfffffe102d95b3a0
blst_meta_free() at blst_meta_free+0x102/frame 0xfffffe102d95b3e0
blst_meta_free() at blst_meta_free+0x102/frame 0xfffffe102d95b420
blst_meta_free() at blst_meta_free+0x102/frame 0xfffffe102d95b460
blist_free() at blist_free+0x2e/frame 0xfffffe102d95b480
swp_pager_freeswapspace() at swp_pager_freeswapspace+0x8a/frame 0xfffffe102d95b4a0
swp_pager_meta_free_all() at swp_pager_meta_free_all+0xbb/frame 0xfffffe102d95b4f0
swap_pager_dealloc() at swap_pager_dealloc+0x115/frame 0xfffffe102d95b510
vm_object_terminate() at vm_object_terminate+0x27b/frame 0xfffffe102d95b560
vm_object_deallocate() at vm_object_deallocate+0x412/frame 0xfffffe102d95b5c0
vm_map_process_deferred() at vm_map_process_deferred+0x7f/frame 0xfffffe102d95b5e0
vm_map_remove() at vm_map_remove+0xc6/frame 0xfffffe102d95b610
vmspace_exit() at vmspace_exit+0xd3/frame 0xfffffe102d95b650
exit1() at exit1+0x5ad/frame 0xfffffe102d95b6c0
sigexit() at sigexit+0xdaf/frame 0xfffffe102d95b9a0
postsig() at postsig+0x336/frame 0xfffffe102d95ba70
ast() at ast+0x4c7/frame 0xfffffe102d95bab0
doreti_ast() at doreti_ast+0x1f/frame 0x7fffffffded0
KDB: enter: panic
[ thread pid 3581 tid 100238 ]
Stopped at      kdb_enter+0x3b: movq    $0,kdb_why
db> x/s version
version:        FreeBSD 13.0-CURRENT #5 r349777: Tue Jul  9 11:37:16 CEST 2019\012    pho@mercat1.netperf.freebsd.org:/usr/src/sys/amd64/compile/MEMGUARD\012
db>

The same test works fine on r349776.

Revision Contents
Changeset List

PathSize
kern/
98 lines
vm/
12 lines

Diff 58876

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kern/subr_blist.c

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vm/swap_pager.c

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