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From: Minchan Kim <minchan@kernel.org>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Subject: Re: [PATCH v7 11/12] zsmalloc: page migration support
Date: Thu, 2 Jun 2016 09:25:19 +0900
Message-ID: <20160602002519.GB1736@bbox> (raw)
In-Reply-To: <574EEC96.8050805@suse.cz>

On Wed, Jun 01, 2016 at 04:09:26PM +0200, Vlastimil Babka wrote:
> On 06/01/2016 01:21 AM, Minchan Kim wrote:
> 
> [...]
> 
> > 
> > Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
> > Signed-off-by: Minchan Kim <minchan@kernel.org>
> 
> I'm not that familiar with zsmalloc, so this is not a full review. I was
> just curious how it's handling the movable migration API, and stumbled
> upon some things pointed out below.
> 
> > @@ -252,16 +276,23 @@ struct zs_pool {
> >   */
> >  #define FULLNESS_BITS	2
> >  #define CLASS_BITS	8
> > +#define ISOLATED_BITS	3
> > +#define MAGIC_VAL_BITS	8
> >  
> >  struct zspage {
> >  	struct {
> >  		unsigned int fullness:FULLNESS_BITS;
> >  		unsigned int class:CLASS_BITS;
> > +		unsigned int isolated:ISOLATED_BITS;
> > +		unsigned int magic:MAGIC_VAL_BITS;
> 
> This magic seems to be only tested via VM_BUG_ON, so it's presence
> should be also guarded by #ifdef DEBUG_VM, no?

Thanks for the point.

Then, I want to change it to BUG_ON because struct zspage corruption
is really risky to work rightly and want to catch on it in real product
which disable CONFIG_DEBUG_VM for a while until make the feature stable.

> 
> > @@ -999,6 +1141,8 @@ static struct zspage *alloc_zspage(struct zs_pool *pool,
> >  		return NULL;
> >  
> >  	memset(zspage, 0, sizeof(struct zspage));
> > +	zspage->magic = ZSPAGE_MAGIC;
> 
> Same here.
> 
> > +int zs_page_migrate(struct address_space *mapping, struct page *newpage,
> > +		struct page *page, enum migrate_mode mode)
> > +{
> > +	struct zs_pool *pool;
> > +	struct size_class *class;
> > +	int class_idx;
> > +	enum fullness_group fullness;
> > +	struct zspage *zspage;
> > +	struct page *dummy;
> > +	void *s_addr, *d_addr, *addr;
> > +	int offset, pos;
> > +	unsigned long handle, head;
> > +	unsigned long old_obj, new_obj;
> > +	unsigned int obj_idx;
> > +	int ret = -EAGAIN;
> > +
> > +	VM_BUG_ON_PAGE(!PageMovable(page), page);
> > +	VM_BUG_ON_PAGE(!PageIsolated(page), page);
> > +
> > +	zspage = get_zspage(page);
> > +
> > +	/* Concurrent compactor cannot migrate any subpage in zspage */
> > +	migrate_write_lock(zspage);
> > +	get_zspage_mapping(zspage, &class_idx, &fullness);
> > +	pool = mapping->private_data;
> > +	class = pool->size_class[class_idx];
> > +	offset = get_first_obj_offset(class, get_first_page(zspage), page);
> > +
> > +	spin_lock(&class->lock);
> > +	if (!get_zspage_inuse(zspage)) {
> > +		ret = -EBUSY;
> > +		goto unlock_class;
> > +	}
> > +
> > +	pos = offset;
> > +	s_addr = kmap_atomic(page);
> > +	while (pos < PAGE_SIZE) {
> > +		head = obj_to_head(page, s_addr + pos);
> > +		if (head & OBJ_ALLOCATED_TAG) {
> > +			handle = head & ~OBJ_ALLOCATED_TAG;
> > +			if (!trypin_tag(handle))
> > +				goto unpin_objects;
> > +		}
> > +		pos += class->size;
> > +	}
> > +
> > +	/*
> > +	 * Here, any user cannot access all objects in the zspage so let's move.
> > +	 */
> > +	d_addr = kmap_atomic(newpage);
> > +	memcpy(d_addr, s_addr, PAGE_SIZE);
> > +	kunmap_atomic(d_addr);
> > +
> > +	for (addr = s_addr + offset; addr < s_addr + pos;
> > +					addr += class->size) {
> > +		head = obj_to_head(page, addr);
> > +		if (head & OBJ_ALLOCATED_TAG) {
> > +			handle = head & ~OBJ_ALLOCATED_TAG;
> > +			if (!testpin_tag(handle))
> > +				BUG();
> > +
> > +			old_obj = handle_to_obj(handle);
> > +			obj_to_location(old_obj, &dummy, &obj_idx);
> > +			new_obj = (unsigned long)location_to_obj(newpage,
> > +								obj_idx);
> > +			new_obj |= BIT(HANDLE_PIN_BIT);
> > +			record_obj(handle, new_obj);
> > +		}
> > +	}
> > +
> > +	replace_sub_page(class, zspage, newpage, page);
> > +	get_page(newpage);
> > +
> > +	dec_zspage_isolation(zspage);
> > +
> > +	/*
> > +	 * Page migration is done so let's putback isolated zspage to
> > +	 * the list if @page is final isolated subpage in the zspage.
> > +	 */
> > +	if (!is_zspage_isolated(zspage))
> > +		putback_zspage(class, zspage);
> > +
> > +	reset_page(page);
> > +	put_page(page);
> > +	page = newpage;
> > +
> > +	ret = 0;
> > +unpin_objects:
> > +	for (addr = s_addr + offset; addr < s_addr + pos;
> > +						addr += class->size) {
> > +		head = obj_to_head(page, addr);
> > +		if (head & OBJ_ALLOCATED_TAG) {
> > +			handle = head & ~OBJ_ALLOCATED_TAG;
> > +			if (!testpin_tag(handle))
> > +				BUG();
> > +			unpin_tag(handle);
> > +		}
> > +	}
> > +	kunmap_atomic(s_addr);
> 
> The above seems suspicious to me. In the success case, page points to
> newpage, but s_addr is still the original one?

s_addr is virtual adress of old page by kmap_atomic so page pointer of
new page doesn't matter.

> 
> Vlastimil
> 
> --
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  reply index

Thread overview: 49+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-05-31 23:21 [PATCH v7 00/12] Support non-lru page migration Minchan Kim
2016-05-31 23:21 ` [PATCH v7 01/12] mm: use put_page to free page instead of putback_lru_page Minchan Kim
2016-05-31 23:21 ` [PATCH v7 02/12] mm: migrate: support non-lru movable page migration Minchan Kim
2016-05-31 23:21 ` [PATCH v7 03/12] mm: balloon: use general non-lru movable page feature Minchan Kim
2016-05-31 23:21 ` [PATCH v7 04/12] zsmalloc: keep max_object in size_class Minchan Kim
2016-05-31 23:21 ` [PATCH v7 05/12] zsmalloc: use bit_spin_lock Minchan Kim
2016-05-31 23:21 ` [PATCH v7 06/12] zsmalloc: use accessor Minchan Kim
2016-05-31 23:21 ` [PATCH v7 07/12] zsmalloc: factor page chain functionality out Minchan Kim
2016-05-31 23:21 ` [PATCH v7 08/12] zsmalloc: introduce zspage structure Minchan Kim
2016-05-31 23:21 ` [PATCH v7 09/12] zsmalloc: separate free_zspage from putback_zspage Minchan Kim
2016-05-31 23:21 ` [PATCH v7 10/12] zsmalloc: use freeobj for index Minchan Kim
2016-05-31 23:21 ` [PATCH v7 11/12] zsmalloc: page migration support Minchan Kim
2016-06-01 14:09   ` Vlastimil Babka
2016-06-02  0:25     ` Minchan Kim [this message]
2016-06-02 11:44       ` Vlastimil Babka
2016-06-01 21:39   ` Andrew Morton
2016-06-02  0:15     ` Minchan Kim
     [not found]   ` <CGME20170119001317epcas1p188357c77e1f4ff08b6d3dcb76dedca06@epcas1p1.samsung.com>
2017-01-19  0:13     ` Chulmin Kim
2017-01-19  2:44       ` Minchan Kim
2017-01-19  3:39         ` Chulmin Kim
2017-01-19  6:21           ` Minchan Kim
2017-01-19  8:16             ` Chulmin Kim
2017-01-23  5:22               ` Minchan Kim
2017-01-23  5:30                 ` Sergey Senozhatsky
2017-01-23  5:40                   ` Minchan Kim
2017-01-25  4:06                     ` Chulmin Kim
2017-01-25  4:25                       ` Sergey Senozhatsky
2017-01-25  5:26                       ` Minchan Kim
2017-01-26 17:04                         ` Dan Streetman
2017-01-31  0:10                           ` Minchan Kim
2017-01-31 13:09                             ` Dan Streetman
2017-02-01  6:51                               ` Minchan Kim
2017-02-01 19:38                                 ` Dan Streetman
2017-02-02  8:48                               ` Minchan Kim
2016-05-31 23:21 ` [PATCH v7 12/12] zram: use __GFP_MOVABLE for memory allocation Minchan Kim
2016-06-01 21:41 ` [PATCH v7 00/12] Support non-lru page migration Andrew Morton
2016-06-01 22:40   ` Daniel Vetter
2016-06-02  0:36   ` Minchan Kim
2016-06-15  7:59 ` Sergey Senozhatsky
2016-06-15 23:12   ` Minchan Kim
2016-06-16  2:48     ` Sergey Senozhatsky
2016-06-16  2:58       ` Minchan Kim
2016-06-16  4:23         ` Sergey Senozhatsky
2016-06-16  4:47           ` Minchan Kim
2016-06-16  5:22             ` Sergey Senozhatsky
2016-06-16  6:47               ` Minchan Kim
2016-06-16  8:42                 ` Sergey Senozhatsky
2016-06-16 10:09                   ` Minchan Kim
2016-06-17  7:28                     ` Joonsoo Kim

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