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DateWed, 08 Aug 2007 00:00:11 +0530
FromVaidyanathan Srinivasan <>
SubjectRe: [-mm PATCH 6/9] Memory controller add per container LRU and reclaim (v4)
Vaidyanathan Srinivasan wrote:
> > YAMAMOTO Takashi wrote:>>> +unsigned long mem_container_isolate_pages(unsigned long nr_to_scan,
>>> +					struct list_head *dst,>>> +					unsigned long *scanned, int order,>>> +					int mode, struct zone *z,>>> +					struct mem_container *mem_cont,>>> +					int active)>>> +{>>> +	unsigned long nr_taken = 0;>>> +	struct page *page;>>> +	unsigned long scan;>>> +	LIST_HEAD(mp_list);>>> +	struct list_head *src;>>> +	struct meta_page *mp;>>> +>>> +	if (active)>>> +		src = &mem_cont->active_list;>>> +	else>>> +		src = &mem_cont->inactive_list;>>> +>>> +	for (scan = 0; scan < nr_to_scan && !list_empty(src); scan++) {
>>> +		mp = list_entry(src->prev, struct meta_page, lru);>> what prevents another thread from freeing mp here?> > mem_cont->lru_lock protects the list and validity of mp.  If we hold
> mem_cont->lru_lock for this entire loop, then we preserve the validity
> of mp.  However that will be holding up container charge and uncharge.
> > This entire routing is called with zone->lru_lock held by the caller.
>  So within a zone, this routine is serialized.
> 
> However page uncharge may race with isolate page.  But will that lead
> to any corruption of the list?  We may be holding the lock for too
> much time just to be on the safe side.
> 
> Please allow us some time to verify whether this is indeed inadequate
> locking that will lead to corruption of the list.

I did few runs and checked for ref_cnt on meta_page and there seems to
be a race between isolate pages and uncharge.  We will probably have
to increase the ref_cnt on meta_page while we are isolating it.  I am
trying to see if we can solve the problem by manipulating the ref_cnt
on the meta_page.

--Vaidy

> Thanks for pointing out this situation.> --Vaidy> >>> +		spin_lock(&mem_cont->lru_lock);>>> +		if (mp)>>> +			page = mp->page;>>> +		spin_unlock(&mem_cont->lru_lock);>>> +		if (!mp)>>> +			continue;>> YAMAMOTO Takashi>> _______________________________________________>> Containers mailing list>> Containers@lists.linux-foundation.org>> https://lists.linux-foundation.org/mailman/listinfo/containers>>> _______________________________________________> Containers mailing list> Containers@lists.linux-foundation.org> https://lists.linux-foundation.org/mailman/listinfo/containers> 
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