linux-kernel - Re: [RFC v2][PATCH 4/9] Memory management

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Message-ID: <20080821095316.GH581@hawkmoon.kerlabs.com>
Date:	Thu, 21 Aug 2008 11:53:16 +0200
From:	Louis Rilling <Louis.Rilling@...labs.com>
To:	Oren Laadan <orenl@...columbia.edu>
Cc:	dave@...ux.vnet.ibm.com, arnd@...db.de, jeremy@...p.org,
	linux-kernel@...r.kernel.org, containers@...ts.linux-foundation.org
Subject: Re: [RFC v2][PATCH 4/9] Memory management - dump state

On Wed, Aug 20, 2008 at 11:05:15PM -0400, Oren Laadan wrote:
>
> For each VMA, there is a 'struct cr_vma'; if the VMA is file-mapped,
> it will be followed by the file name.  The cr_vma->npages will tell
> how many pages were dumped for this VMA.  Then it will be followed
> by the actual data: first a dump of the addresses of all dumped
> pages (npages entries) followed by a dump of the contents of all
> dumped pages (npages pages). Then will come the next VMA and so on.

[...]

> diff --git a/checkpoint/ckpt_mem.c b/checkpoint/ckpt_mem.c
> new file mode 100644
> index 0000000..a23aa29
> --- /dev/null
> +++ b/checkpoint/ckpt_mem.c

[...]

> +/**
> + * cr_vma_fill_pgarr - fill a page-array with addr/page tuples for a vma
> + * @ctx - checkpoint context
> + * @pgarr - page-array to fill
> + * @vma - vma to scan
> + * @start - start address (updated)
> + */
> +static int cr_vma_fill_pgarr(struct cr_ctx *ctx, struct cr_pgarr *pgarr,
> +			     struct vm_area_struct *vma, unsigned long *start)
> +{
> +	unsigned long end = vma->vm_end;
> +	unsigned long addr = *start;
> +	struct page **pagep;
> +	unsigned long *addrp;
> +	int cow, nr, ret = 0;
> +
> +	nr = pgarr->nleft;
> +	pagep = &pgarr->pages[pgarr->nused];
> +	addrp = &pgarr->addrs[pgarr->nused];
> +	cow = !!vma->vm_file;
> +
> +	while (addr < end) {
> +		struct page *page;
> +
> +		/* simplified version of get_user_pages(): already have vma,
> +		* only need FOLL_TOUCH, and (for now) ignore fault stats */
> +
> +		cond_resched();
> +		while (!(page = follow_page(vma, addr, FOLL_TOUCH))) {
> +			ret = handle_mm_fault(vma->vm_mm, vma, addr, 0);
> +			if (ret & VM_FAULT_ERROR) {
> +				if (ret & VM_FAULT_OOM)
> +					ret = -ENOMEM;
> +				else if (ret & VM_FAULT_SIGBUS)
> +					ret = -EFAULT;
> +				else
> +					BUG();
> +				break;
> +			}

+			ret = 0;

> +			cond_resched();
> +		}
> +
> +		if (IS_ERR(page)) {
> +			ret = PTR_ERR(page);
> +			break;
> +		}

Need to check ret here:

+ 		if (ret)
			break;

> +
> +		if (page == ZERO_PAGE(0))
> +			page = NULL;	/* zero page: ignore */
> +		else if (cow && page_mapping(page) != NULL)
> +			page = NULL;	/* clean cow: ignore */
> +		else {
> +			get_page(page);
> +			*(addrp++) = addr;
> +			*(pagep++) = page;
> +			if (--nr == 0) {
> +				addr += PAGE_SIZE;
> +				break;
> +			}
> +		}
> +
> +		addr += PAGE_SIZE;
> +	}
> +
> +	if (unlikely(ret < 0)) {
> +		nr = pgarr->nleft - nr;
> +		while (nr--)
> +			page_cache_release(*(--pagep));
> +		return ret;
> +	}
> +
> +	*start = addr;
> +	return (pgarr->nleft - nr);
> +}

[...]

Thanks,

Louis

-- 
Dr Louis Rilling			Kerlabs
Skype: louis.rilling			Batiment Germanium
Phone: (+33|0) 6 80 89 08 23		80 avenue des Buttes de Coesmes
http://www.kerlabs.com/			35700 Rennes

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