linux-kernel - Re: [PATCH 1/5] staging: zsmalloc: zsmalloc memory allocation library

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Date:	Wed, 11 Jan 2012 11:45:11 -0600
From:	Seth Jennings <sjenning@...ux.vnet.ibm.com>
To:	Dan Magenheimer <dan.magenheimer@...cle.com>
CC:	Greg Kroah-Hartman <gregkh@...e.de>,
	Nitin Gupta <ngupta@...are.org>,
	Brian King <brking@...ux.vnet.ibm.com>,
	Konrad Wilk <konrad.wilk@...cle.com>,
	Dave Hansen <dave@...ux.vnet.ibm.com>, linux-mm@...ck.org,
	devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/5] staging: zsmalloc: zsmalloc memory allocation library

On 01/11/2012 11:19 AM, Dan Magenheimer wrote:
>> From: Seth Jennings [mailto:sjenning@...ux.vnet.ibm.com]
>> Subject: [PATCH 1/5] staging: zsmalloc: zsmalloc memory allocation library
>>
>> From: Nitin Gupta <ngupta@...are.org>
>>
>> This patch creates a new memory allocation library named
>> zsmalloc.
>>
>> +/*
>> + * Allocate a zspage for the given size class
>> + */
>> +static struct page *alloc_zspage(struct size_class *class, gfp_t flags)
>> +{
>> +	int i, error;
>> +	struct page *first_page = NULL;
>> +
>> +	/*
>> +	 * Allocate individual pages and link them together as:
>> +	 * 1. first page->private = first sub-page
>> +	 * 2. all sub-pages are linked together using page->lru
>> +	 * 3. each sub-page is linked to the first page using page->first_page
>> +	 *
>> +	 * For each size class, First/Head pages are linked together using
>> +	 * page->lru. Also, we set PG_private to identify the first page
>> +	 * (i.e. no other sub-page has this flag set) and PG_private_2 to
>> +	 * identify the last page.
>> +	 */
>> +	error = -ENOMEM;
>> +	for (i = 0; i < class->zspage_order; i++) {
>> +		struct page *page, *prev_page;
>> +
>> +		page = alloc_page(flags);
> 
> Hmmm... I thought we agreed offlist that the new allocator API would
> provide for either preloads or callbacks (which may differ per pool)
> instead of directly allocating raw pages from the kernel.  The caller
> (zcache or ramster or ???) needs to be able to somehow manage maximum
> memory capacity to avoid OOMs.
> 
> Or am I missing the code that handles that?

No, you aren't missing it; it's not there.  And I agree that we
should add that.

However, the existing allocator, xvmalloc, doesn't support callback
functionality either.  Would it be simpler to add the that as 
a separate patch, that way we can keep the changes to zcache/zram
in this patchset isolated to just changing the xvmalloc calls to 
zsmalloc calls?

--
Seth

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