linux-kernel - Re: [RFC v4][PATCH 5/9] Memory managemnet (restore)

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Date:	Wed, 10 Sep 2008 15:48:50 -0400
From:	Oren Laadan <orenl@...columbia.edu>
To:	Dave Hansen <dave@...ux.vnet.ibm.com>
CC:	containers@...ts.linux-foundation.org, jeremy@...p.org,
	linux-kernel@...r.kernel.org, arnd@...db.de
Subject: Re: [RFC v4][PATCH 5/9] Memory managemnet (restore)



Dave Hansen wrote:
> On Tue, 2008-09-09 at 03:42 -0400, Oren Laadan wrote:
>> +/**
>> + * cr_vma_read_pages_vaddrs - read addresses of pages to page-array chain
>> + * @ctx - restart context
>> + * @npages - number of pages
>> + */
>> +static int cr_vma_read_pages_vaddrs(struct cr_ctx *ctx, int npages)
>> +{
>> +	struct cr_pgarr *pgarr;
>> +	int nr, ret;
>> +
>> +	while (npages) {
>> +		pgarr = cr_pgarr_prep(ctx);
>> +		if (!pgarr)
>> +			return -ENOMEM;
>> +		nr = min(npages, (int) pgarr->nr_free);
>> +		ret = cr_kread(ctx, pgarr->vaddrs, nr * sizeof(unsigned long));
>> +		if (ret < 0)
>> +			return ret;
>> +		pgarr->nr_free -= nr;
>> +		pgarr->nr_used += nr;
>> +		npages -= nr;
>> +	}
>> +	return 0;
>> +}
> 
> cr_pgarr_prep() can return a partially full pgarr, right?  Won't the
> cr_kread() always start at the beginning of the pgarr->vaddrs[] array?
> Seems to me like it will clobber things from the last call.

Note that 'nr' is either equal to ->nr_free - in which case we consume
the entire 'pgarr' vaddr array such that the next call to cr_pgarr_prep()
will get a fresh one, or is smaller than ->nr_free - in which case that
is the last iteration of the loop anyhow, so it won't be clobbered.

Also, after we return - our caller, cr_vma_read_pages(), resets the state
of the page-array chain by calling cr_pgarr_reset().

Oren.
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