The minimum free RAM was about 9.8-11MB (matching your guestimate) and
kswapd seemed to behave the same as the watermark patch. The results of
top were basically the same, so I'm omitting it.
However, I do have some profiling numbers, thanks to Marcelo. Attached
are numbers from "readprofile | sort -nr +2 | head -20". I think the
pre4 numbers point to shrink_cache, prune_icache, and statm_pgd_range.
The other two might have significance for wizards, but statistically
don't stand out to me, except maybe statm_pgd_range.
I reset the counters just before starting Oracle and the stress test. I
think a -pre7 with a blessed patch would be good, since my testing was
very narrow.
I'll test new kernels as I hear new info.
Thanks much!
-- Ken. brownfld@irridia.com
2.4.15-pre4 with your original patch: (shorter time period since the machine went to hell fast) (matches vanilla behaviour)
164536 default_idle 3164.1538 101562 shrink_cache 113.8587 3683 prune_icache 13.5404 3034 file_read_actor 12.2339 914 DAC960_BA_InterruptHandler 5.5732 1128 statm_pgd_range 2.9072 40 page_cache_release 0.8333 31 add_page_to_hash_queue 0.5167 89 page_cache_read 0.4363 25 remove_inode_page 0.4167 26 unlock_page 0.3095 509 __make_request 0.3008 66 smp_call_function 0.2946 21 set_bh_page 0.2917 9 __brelse 0.2812 90 try_to_free_buffers 0.2778 13 mark_page_accessed 0.2708 8 __free_pages 0.2500 43 get_hash_table 0.2443 42 activate_page 0.2234
2.4.15-pre6 with watermark patch:
1617446 default_idle 31104.7308 27599 DAC960_BA_InterruptHandler 168.2866 38918 file_read_actor 156.9274 528 page_cache_release 11.0000 554 add_page_to_hash_queue 9.2333 15487 __make_request 9.1531 3453 statm_pgd_range 8.8995 514 remove_inode_page 8.5667 1453 blk_init_free_list 7.2650 377 set_bh_page 5.2361 898 page_cache_read 4.4020 590 add_to_page_cache_unique 4.3382 136 __brelse 4.2500 1120 kmem_cache_alloc 3.8356 628 kunmap_high 3.7381 1189 try_to_free_buffers 3.6698 625 get_hash_table 3.5511 439 lru_cache_add 3.4297 1715 rmqueue 3.0194 105 remove_wait_queue 2.9167
2.4.15-pre6 with Linus patch:
1249875 default_idle 24036.0577 65324 file_read_actor 263.4032 36979 DAC960_BA_InterruptHandler 225.4817 9809 statm_pgd_range 25.2809 1039 page_cache_release 21.6458 994 add_page_to_hash_queue 16.5667 922 remove_inode_page 15.3667 2409 blk_init_free_list 12.0450 20159 __make_request 11.9143 1198 lru_cache_add 9.3594 1628 page_cache_read 7.9804 987 add_to_page_cache_unique 7.2574 2202 try_to_free_buffers 6.7963 1038 get_unused_buffer_head 6.6538 484 unlock_page 5.7619 3182 rmqueue 5.6021 874 kunmap_high 5.2024 164 __brelse 5.1250 900 get_hash_table 5.1136 357 set_bh_page 4.9583
On Mon, Nov 19, 2001 at 03:52:44PM -0800, Linus Torvalds wrote: | | On Mon, 19 Nov 2001, Ken Brownfield wrote: | > | > I went straight to the aa patch, and it looks like it either fixes the | > problem or (because of the side-effects Linus mentioned) otherwise | > prevents the issue: | | So is this pre6aa1, or pre6 + just the watermark patch? | | > The machine went into swap immediately when the page cache stopped | > growing and hovered at 100-400MB. Also, in my experience the page cache | > will grow until there's only 5ishMB of free RAM, but with the aa patch | > it looks like it stops at 320MB or maybe 10% of RAM. Was that the aa | > patch, or part of -pre6? | | That was the watermarking. The way Andrea did it, the page cache will | basically refuse to touch as much of the "normal" page zone, because it | would prefer to allocate more from highmem.. | | I think it's excessive to have 320MB free memory, though, that's just | an insane waste. I suspect that the real number should be somewhere | between the old behaviour and the new one. You can tweak the behaviour of | andrea's kernel by changing the "reserved" page numbers, but I'd like to | hear whether my simpler approach works too.. | | > The Oracle SGA is set to ~522MB, with nothing else running except a | > couple of sshds, getty, etc. Now that I'm looking, 2.8GB page cache | > plus 328MB free adds up to about 3.1GB of RAM -- where does the 512MB | > shared memory segment fit? Is it being swapped out in deference to page | > cache? | | Shared memory actually uses the page cache too, so it will be accounted | for in the 2.8GB number. | | Anyway, can you try plain vanilla pre6, with the appended patch? This is | my suggested simplified version of what Andrea tried to do, and it should | try to keep only a few extra megs of memory free in the low memory | regions, not 300+ MB. | | (and the profiling would be interesting regardless, but I think Andrea did | find the real problem, his fix just seems a bit of an overkill ;) | | Linus
| diff -u --recursive --new-file pre6/linux/mm/page_alloc.c linux/mm/page_alloc.c | --- pre6/linux/mm/page_alloc.c Sat Nov 17 19:07:43 2001 | +++ linux/mm/page_alloc.c Mon Nov 19 15:13:36 2001 | @@ -299,29 +299,26 @@ | return page; | } | | -static inline unsigned long zone_free_pages(zone_t * zone, unsigned int order) | -{ | - long free = zone->free_pages - (1UL << order); | - return free >= 0 ? free : 0; | -} | - | /* | * This is the 'heart' of the zoned buddy allocator: | */ | struct page * __alloc_pages(unsigned int gfp_mask, unsigned int order, zonelist_t *zonelist) | { | + unsigned long min; | zone_t **zone, * classzone; | struct page * page; | int freed; | | zone = zonelist->zones; | classzone = *zone; | + min = 1UL << order; | for (;;) { | zone_t *z = *(zone++); | if (!z) | break; | | - if (zone_free_pages(z, order) > z->pages_low) { | + min += z->pages_low; | + if (z->free_pages > min) { | page = rmqueue(z, order); | if (page) | return page; | @@ -334,16 +331,18 @@ | wake_up_interruptible(&kswapd_wait); | | zone = zonelist->zones; | + min = 1UL << order; | for (;;) { | - unsigned long min; | + unsigned long local_min; | zone_t *z = *(zone++); | if (!z) | break; | | - min = z->pages_min; | + local_min = z->pages_min; | if (!(gfp_mask & __GFP_WAIT)) | - min >>= 2; | - if (zone_free_pages(z, order) > min) { | + local_min >>= 2; | + min += local_min; | + if (z->free_pages > min) { | page = rmqueue(z, order); | if (page) | return page; | @@ -376,12 +375,14 @@ | return page; | | zone = zonelist->zones; | + min = 1UL << order; | for (;;) { | zone_t *z = *(zone++); | if (!z) | break; | | - if (zone_free_pages(z, order) > z->pages_min) { | + min += z->pages_min; | + if (z->free_pages > min) { | page = rmqueue(z, order); | if (page) | return page;
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