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 [thread overview]
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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next prev parent reply other threads:[~2016-06-02 0:24 UTC|newest]
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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