Re: [2.4] heavy-load under swap space shortage

[Marcelo Tosatti <marcelo.tosatti@cyclades.com>]

Andrea, Hugh, Jun'ichi,

I think we can merge this patch.

Its very safe - default behaviour unchanged. 

Jun, are you willing to do another test for us if this gets merged
in v2.4.27-pre4 ?

Maybe we should document the VM tunables somewhere outside source code
(Documentation/) ?

On Wed, Mar 10, 2004 at 07:57:07PM +0900, j-nomura@ce.jp.nec.com wrote:
> After discussion with Hugh and recommendation from Andrea,
> it turns out that Andrea's 05_vm_22_vm-anon-lru-3 in 2.4.23aa2 solves
> the problem.
> ftp://ftp.kernel.org/pub/linux/kernel/people/andrea/kernels/v2.4/2.4.23aa2/05_vm_22_vm-anon-lru-3
> 
> The patch adds a sysctl which accelerate the performance on
> huge memory machine. It doesn't affect anything if turned off.
> 
> Marcelo, could you apply this to 2.4.26-pre?
> (I attached the slightly modified patch in which the feature is turned
> off by default and which is cleanly applied to bk tree.)
> 
> 
> My test case was:
>   - there is a process with large anonymous mapping
>   - there are large amount of page caches and active I/O processes
>   - there are not much of file mappings
> 
> So the problem happens in this way:
>   - shrink_cache tries scanning inactive list in which most of pages
>     are anonymous mapped
>   - it soon fall into swap_out because of too many anonymous pages
>   - when no free swap space, it hardly frees anything
>   - it retries again but soon calls swap_out again and again
> 
> Without the patch, snapshot of readprofile looks like:
>    3590781 total
>    3289271 swap_out
>     212029 smp_call_function
>      22598 shrink_cache
>      21833 lru_cache_add
>       7787 get_user_pages
> 
> Most of the time was spent in swap_out. (contention on pagetable_lock)
> 
> After applying the patch, the snapshot is like:
>     17420 total
>      3929 copy_page
>      3677 statm_pgd_range
>      1317 try_to_free_buffers
>      1312 __copy_user
>       593 scsi_make_request
> 
> Best regards.
> --
> NOMURA, Jun'ichi <j-nomura@ce.jp.nec.com>

> --- linux/include/linux/swap.h	2004/02/19 04:12:39	1.1.1.26
> +++ linux/include/linux/swap.h	2004/03/10 10:09:11
> @@ -116,7 +116,7 @@ extern void swap_setup(void);
>  extern wait_queue_head_t kswapd_wait;
>  extern int FASTCALL(try_to_free_pages_zone(zone_t *, unsigned int));
>  extern int FASTCALL(try_to_free_pages(unsigned int));
> -extern int vm_vfs_scan_ratio, vm_cache_scan_ratio, vm_lru_balance_ratio, vm_passes, vm_gfp_debug, vm_mapped_ratio;
> +extern int vm_vfs_scan_ratio, vm_cache_scan_ratio, vm_lru_balance_ratio, vm_passes, vm_gfp_debug, vm_mapped_ratio, vm_anon_lru;
>  
>  /* linux/mm/page_io.c */
>  extern void rw_swap_page(int, struct page *);
> --- linux/include/linux/sysctl.h	2004/02/19 04:12:39	1.1.1.23
> +++ linux/include/linux/sysctl.h	2004/03/10 10:09:11
> @@ -156,6 +156,7 @@ enum
>  	VM_MAPPED_RATIO=20,     /* amount of unfreeable pages that triggers swapout */
>  	VM_LAPTOP_MODE=21,	/* kernel in laptop flush mode */
>  	VM_BLOCK_DUMP=22,	/* dump fs activity to log */
> +	VM_ANON_LRU=23,		/* immediatly insert anon pages in the vm page lru */
>  };
>  
>  
> --- linux/kernel/sysctl.c	2003/12/02 04:48:47	1.1.1.22
> +++ linux/kernel/sysctl.c	2004/03/10 10:09:12
> @@ -287,6 +287,8 @@ static ctl_table vm_table[] = {
>  	 &vm_cache_scan_ratio, sizeof(int), 0644, NULL, &proc_dointvec},
>  	{VM_MAPPED_RATIO, "vm_mapped_ratio", 
>  	 &vm_mapped_ratio, sizeof(int), 0644, NULL, &proc_dointvec},
> +	{VM_ANON_LRU, "vm_anon_lru", 
> +	 &vm_anon_lru, sizeof(int), 0644, NULL, &proc_dointvec},
>  	{VM_LRU_BALANCE_RATIO, "vm_lru_balance_ratio", 
>  	 &vm_lru_balance_ratio, sizeof(int), 0644, NULL, &proc_dointvec},
>  	{VM_PASSES, "vm_passes", 
> --- linux/mm/memory.c	2003/12/02 04:48:47	1.1.1.31
> +++ linux/mm/memory.c	2004/03/10 10:09:12
> @@ -984,7 +984,8 @@ static int do_wp_page(struct mm_struct *
>  		if (PageReserved(old_page))
>  			++mm->rss;
>  		break_cow(vma, new_page, address, page_table);
> -		lru_cache_add(new_page);
> +		if (vm_anon_lru)
> +			lru_cache_add(new_page);
>  
>  		/* Free the old page.. */
>  		new_page = old_page;
> @@ -1215,7 +1216,8 @@ static int do_anonymous_page(struct mm_s
>  		mm->rss++;
>  		flush_page_to_ram(page);
>  		entry = pte_mkwrite(pte_mkdirty(mk_pte(page, vma->vm_page_prot)));
> -		lru_cache_add(page);
> +		if (vm_anon_lru)
> +			lru_cache_add(page);
>  		mark_page_accessed(page);
>  	}
>  
> @@ -1270,7 +1272,8 @@ static int do_no_page(struct mm_struct *
>  		}
>  		copy_user_highpage(page, new_page, address);
>  		page_cache_release(new_page);
> -		lru_cache_add(page);
> +		if (vm_anon_lru)
> +			lru_cache_add(page);
>  		new_page = page;
>  	}
>  
> --- linux/mm/vmscan.c	2004/02/19 04:12:33	1.1.1.32
> +++ linux/mm/vmscan.c	2004/03/10 10:09:13
> @@ -65,6 +65,27 @@ int vm_lru_balance_ratio = 2;
>  int vm_vfs_scan_ratio = 6;
>  
>  /*
> + * "vm_anon_lru" select if to immdiatly insert anon pages in the
> + * lru. Immediatly means as soon as they're allocated during the
> + * page faults.
> + *
> + * If this is set to 0, they're inserted only after the first
> + * swapout.
> + *
> + * Having anon pages immediatly inserted in the lru allows the
> + * VM to know better when it's worthwhile to start swapping
> + * anonymous ram, it will start to swap earlier and it should
> + * swap smoother and faster, but it will decrease scalability
> + * on the >16-ways of an order of magnitude. Big SMP/NUMA
> + * definitely can't take an hit on a global spinlock at
> + * every anon page allocation. So this is off by default.
> + *
> + * Low ram machines that swaps all the time want to turn
> + * this on (i.e. set to 1).
> + */
> +int vm_anon_lru = 1;
> +
> +/*
>   * The swap-out function returns 1 if it successfully
>   * scanned all the pages it was asked to (`count').
>   * It returns zero if it couldn't do anything,