Re: lot of MemAvailable but falling cache and raising PSI

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



works - thanks

Am 22.10.19 um 12:21 schrieb Vlastimil Babka:
> On 10/22/19 12:02 PM, Stefan Priebe - Profihost AG wrote:
>>
>> Am 22.10.19 um 09:48 schrieb Vlastimil Babka:
>>> On 10/22/19 9:41 AM, Stefan Priebe - Profihost AG wrote:
>>>>> Hi, could you try the patch below? I suspect you're hitting a corner
>>>>> case where compaction_suitable() returns COMPACT_SKIPPED for the
>>>>> ZONE_DMA, triggering reclaim even if other zones have plenty of free
>>>>> memory. And should_continue_reclaim() then returns true until twice the
>>>>> requested page size is reclaimed (compact_gap()). That means 4MB
>>>>> reclaimed for each THP allocation attempt, which roughly matches the
>>>>> trace data you preovided previously.
>>>>>
>>>>> The amplification to 4MB should be removed in patches merged for 5.4, so
>>>>> it would be only 32 pages reclaimed per THP allocation. The patch below
>>>>> tries to remove this corner case completely, and it should be more
>>>>> visible on your 5.2.x, so please apply it there.
>>>>>
>>>> is there any reason to not apply that one on top of 4.19?
>>>>
>>>> Greets,
>>>> Stefan
>>>>
>>>
>>> It should work, cherrypicks fine without conflict here.
>>
>> OK but does not work ;-)
>>
>>
>> mm/compaction.c: In function '__compaction_suitable':
>> mm/compaction.c:1451:19: error: implicit declaration of function
>> 'zone_managed_pages'; did you mean 'node_spanned_pages'?
>> [-Werror=implicit-function-declaration]
>>       alloc_flags, zone_managed_pages(zone)))
>>                    ^~~~~~~~~~~~~~~~~~
>>                    node_spanned_pages
> 
> Ah, this?
> 
> ----8<----
> From f1335e1c0d4b74205fc0cc40b5960223d6f1dec7 Mon Sep 17 00:00:00 2001
> From: Vlastimil Babka <vbabka@xxxxxxx>
> Date: Thu, 12 Sep 2019 13:40:46 +0200
> Subject: [PATCH] WIP
> 
> ---
>  include/linux/compaction.h     |  7 ++++++-
>  include/trace/events/mmflags.h |  1 +
>  mm/compaction.c                | 16 +++++++++++++--
>  mm/vmscan.c                    | 36 ++++++++++++++++++++++++----------
>  4 files changed, 47 insertions(+), 13 deletions(-)
> 
> diff --git a/include/linux/compaction.h b/include/linux/compaction.h
> index 68250a57aace..2f3b331c5239 100644
> --- a/include/linux/compaction.h
> +++ b/include/linux/compaction.h
> @@ -17,8 +17,13 @@ enum compact_priority {
>  };
>  
>  /* Return values for compact_zone() and try_to_compact_pages() */
> -/* When adding new states, please adjust include/trace/events/compaction.h */
> +/* When adding new states, please adjust include/trace/events/mmflags.h */
>  enum compact_result {
> +	/*
> +	 * The zone is too small to provide the requested allocation even if
> +	 * fully freed (i.e. ZONE_DMA for THP allocation due to lowmem reserves)
> +	 */
> +	COMPACT_IMPOSSIBLE,
>  	/* For more detailed tracepoint output - internal to compaction */
>  	COMPACT_NOT_SUITABLE_ZONE,
>  	/*
> diff --git a/include/trace/events/mmflags.h b/include/trace/events/mmflags.h
> index a81cffb76d89..d7aa9cece234 100644
> --- a/include/trace/events/mmflags.h
> +++ b/include/trace/events/mmflags.h
> @@ -169,6 +169,7 @@ IF_HAVE_VM_SOFTDIRTY(VM_SOFTDIRTY,	"softdirty"	)		\
>  
>  #ifdef CONFIG_COMPACTION
>  #define COMPACTION_STATUS					\
> +	EM( COMPACT_IMPOSSIBLE,		"impossible")		\
>  	EM( COMPACT_SKIPPED,		"skipped")		\
>  	EM( COMPACT_DEFERRED,		"deferred")		\
>  	EM( COMPACT_CONTINUE,		"continue")		\
> diff --git a/mm/compaction.c b/mm/compaction.c
> index 5079ddbec8f9..7d2299c7faa2 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -1416,6 +1416,7 @@ static enum compact_result compact_finished(struct zone *zone,
>  /*
>   * compaction_suitable: Is this suitable to run compaction on this zone now?
>   * Returns
> + *   COMPACT_IMPOSSIBLE If the allocation would fail even with all pages free
>   *   COMPACT_SKIPPED  - If there are too few free pages for compaction
>   *   COMPACT_SUCCESS  - If the allocation would succeed without compaction
>   *   COMPACT_CONTINUE - If compaction should run now
> @@ -1439,6 +1440,16 @@ static enum compact_result __compaction_suitable(struct zone *zone, int order,
>  								alloc_flags))
>  		return COMPACT_SUCCESS;
>  
> +	/*
> +	 * If the allocation would not succeed even with a fully free zone
> +	 * due to e.g. lowmem reserves, indicate that compaction can't possibly
> +	 * help and it would be pointless to reclaim.
> +	 */
> +	watermark += 1UL << order;
> +	if (!__zone_watermark_ok(zone, 0, watermark, classzone_idx,
> +				 alloc_flags, zone->managed_pages))
> +		return COMPACT_IMPOSSIBLE;
> +
>  	/*
>  	 * Watermarks for order-0 must be met for compaction to be able to
>  	 * isolate free pages for migration targets. This means that the
> @@ -1526,7 +1537,7 @@ bool compaction_zonelist_suitable(struct alloc_context *ac, int order,
>  		available += zone_page_state_snapshot(zone, NR_FREE_PAGES);
>  		compact_result = __compaction_suitable(zone, order, alloc_flags,
>  				ac_classzone_idx(ac), available);
> -		if (compact_result != COMPACT_SKIPPED)
> +		if (compact_result > COMPACT_SKIPPED)
>  			return true;
>  	}
>  
> @@ -1555,7 +1566,8 @@ static enum compact_result compact_zone(struct zone *zone, struct compact_contro
>  	ret = compaction_suitable(zone, cc->order, cc->alloc_flags,
>  							cc->classzone_idx);
>  	/* Compaction is likely to fail */
> -	if (ret == COMPACT_SUCCESS || ret == COMPACT_SKIPPED)
> +	if (ret == COMPACT_SUCCESS || ret == COMPACT_SKIPPED
> +	    || ret == COMPACT_IMPOSSIBLE)
>  		return ret;
>  
>  	/* huh, compaction_suitable is returning something unexpected */
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index b37610c0eac6..7ad331a64fc5 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2849,11 +2849,12 @@ static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc)
>  }
>  
>  /*
> - * Returns true if compaction should go ahead for a costly-order request, or
> - * the allocation would already succeed without compaction. Return false if we
> - * should reclaim first.
> + * Returns 1 if compaction should go ahead for a costly-order request, or the
> + * allocation would already succeed without compaction. Return 0 if we should
> + * reclaim first. Return -1 when compaction can't help at all due to zone being
> + * too small, which means there's no point in reclaim nor compaction.
>   */
> -static inline bool compaction_ready(struct zone *zone, struct scan_control *sc)
> +static inline int compaction_ready(struct zone *zone, struct scan_control *sc)
>  {
>  	unsigned long watermark;
>  	enum compact_result suitable;
> @@ -2861,10 +2862,16 @@ static inline bool compaction_ready(struct zone *zone, struct scan_control *sc)
>  	suitable = compaction_suitable(zone, sc->order, 0, sc->reclaim_idx);
>  	if (suitable == COMPACT_SUCCESS)
>  		/* Allocation should succeed already. Don't reclaim. */
> -		return true;
> +		return 1;
>  	if (suitable == COMPACT_SKIPPED)
>  		/* Compaction cannot yet proceed. Do reclaim. */
> -		return false;
> +		return 0;
> +	if (suitable == COMPACT_IMPOSSIBLE)
> +		/*
> +		 * Compaction can't possibly help. So don't reclaim, but keep
> +		 * checking other zones.
> +		 */
> +		return -1;
>  
>  	/*
>  	 * Compaction is already possible, but it takes time to run and there
> @@ -2910,6 +2917,7 @@ static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
>  
>  	for_each_zone_zonelist_nodemask(zone, z, zonelist,
>  					sc->reclaim_idx, sc->nodemask) {
> +		int compact_ready;
>  		/*
>  		 * Take care memory controller reclaiming has small influence
>  		 * to global LRU.
> @@ -2929,10 +2937,18 @@ static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
>  			 * page allocations.
>  			 */
>  			if (IS_ENABLED(CONFIG_COMPACTION) &&
> -			    sc->order > PAGE_ALLOC_COSTLY_ORDER &&
> -			    compaction_ready(zone, sc)) {
> -				sc->compaction_ready = true;
> -				continue;
> +			    sc->order > PAGE_ALLOC_COSTLY_ORDER) {
> +				compact_ready = compaction_ready(zone, sc);
> +				if (compact_ready == 1) {
> +					sc->compaction_ready = true;
> +					continue;
> +				} else if (compact_ready == -1) {
> +					/*
> +					 * In this zone, neither reclaim nor
> +					 * compaction can help.
> +					 */
> +					continue;
> +				}
>  			}
>  
>  			/*
> 



[Index of Archives]     [Linux ARM Kernel]     [Linux ARM]     [Linux Omap]     [Fedora ARM]     [IETF Annouce]     [Security]     [Bugtraq]     [Linux OMAP]     [Linux MIPS]     [eCos]     [Asterisk Internet PBX]     [Linux API]     [Monitors]

  Powered by Linux