Messages in this thread Patch in this message |  | | Date | Mon, 29 Oct 2001 04:29:38 +0100 | From | Andrea Arcangeli <> | Subject | Re: VM test on 2.4.14pre3aa2 (compared to 2.4.14pre3aa1) |
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On Mon, Oct 29, 2001 at 03:45:46AM +0100, Andrea Arcangeli wrote: > andrea@dev4-000:~> time ./mtest01 -b $[1024*1024*512] -w > PASS ... 536870912 bytes allocated. > > real 1m8.655s > user 0m9.370s > sys 0m2.250s > andrea@dev4-000:~>
new exciting result on exactly the same test (4Ganon mem +512m swap, then started the bench):
andrea@dev4-000:~> time ./mtest01 -b $[1024*1024*512] -w PASS ... 536870912 bytes allocated.
real 0m40.473s user 0m9.290s sys 0m3.860s andrea@dev4-000:~>
(mainline takes 1m 40s, 1 minute more for the same thing)
I guess I cheated this time though :), see the _only_ change that I did to speedup from 68/69 seconds to exactly 40 seconds:
--- 2.4.14pre3aa2/mm/page_io.c.~1~ Tue May 1 19:35:33 2001 +++ 2.4.14pre3aa2/mm/page_io.c Mon Oct 29 03:58:23 2001 @@ -43,10 +43,12 @@ struct inode *swapf = 0; int wait = 0; +#if 0 /* Don't allow too many pending pages in flight.. */ if ((rw == WRITE) && atomic_read(&nr_async_pages) > pager_daemon.swap_cluster * (1 << page_cluster)) wait = 1; +#endif if (rw == READ) { ClearPageUptodate(page); @@ -75,10 +77,12 @@ } else { return 0; } +#if 0 if (!wait) { SetPageDecrAfter(page); atomic_inc(&nr_async_pages); } +#endif /* block_size == PAGE_SIZE/zones_used */ brw_page(rw, page, dev, zones, block_size); I found we were hurted by not being able to use the full I/O pipeline like we do for writes.
Now it swapouts constantly and regularly at 12.8 Mbyte/sec (still smooth), the write throttling happens at the PG_launder layer like for MAP_SHARED.
hdparm -t on the swap partition says 27 Mbyte/sec but that's unreal, at least with writes, a cp flood at max runs at 17mbyte/sec on such scsi disk where we also swapout to. Without the above change it swapouts at 7.5 Mbyte/sec instead of 12.8 Mbyte/sec. 12.8Mbyte/sec seems acceptable also considering the pagetable walking etc... more costly than a stright generic_file_write + balance_dirty.
I'm aware of the implications of the above, we may empty the pfmemalloc pool, but that should mostly cause some sched_yields, it still runs stable during this test at least. I'd prefer to fix any places to sched_yield rather than running at 7.5 mbyte/sec.
But my strongest non-cheat (and backwards compatibility, no too risk in 2.4) is that we just don't use the nr_async_pages during pageout to disk of the MAP_SHARED segments, so why should we use it for pageout of the anonymous memory that doesn't even need to pass through the fs? (in most setups with a proper swap partition) As far as MAP_SHARED is just correct, page_io.c also shouldn't need it. comments?
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