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Message-ID: <20090416104234.GA6656@linux>
Date: Thu, 16 Apr 2009 12:42:36 +0200
From: Andrea Righi <righi.andrea@...il.com>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc: Ryo Tsuruta <ryov@...inux.co.jp>, menage@...gle.com,
balbir@...ux.vnet.ibm.com, guijianfeng@...fujitsu.com,
agk@...rceware.org, akpm@...ux-foundation.org, axboe@...nel.dk,
baramsori72@...il.com, chlunde@...g.uio.no,
dave@...ux.vnet.ibm.com, dpshah@...gle.com, eric.rannaud@...il.com,
fernando@....ntt.co.jp, taka@...inux.co.jp, lizf@...fujitsu.com,
matt@...ehost.com, dradford@...ehost.com, ngupta@...gle.com,
randy.dunlap@...cle.com, roberto@...it.it, s-uchida@...jp.nec.com,
subrata@...ux.vnet.ibm.com, yoshikawa.takuya@....ntt.co.jp,
containers@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/9] bio-cgroup controller
On Thu, Apr 16, 2009 at 08:58:14AM +0900, KAMEZAWA Hiroyuki wrote:
> On Wed, 15 Apr 2009 15:23:57 +0200
> Andrea Righi <righi.andrea@...il.com> wrote:
>
> > On Wed, Apr 15, 2009 at 09:38:50PM +0900, Ryo Tsuruta wrote:
> > > Hi Andrea and Kamezawa-san,
> > >
> > > > Ryo, it would be great if you can look at this and fix/integrate into
> > > > the mainstream bio-cgroup. Otherwise I can try to to schedule this in my
> > > > work.
> > >
> > > O.K. I'll apply those fixes and post patches as soon as I can.
> > >
> >
> > Very good! I've just tested the bio_cgroup_id inclusion in
> > page_cgroup->flags. I'm posting the patch on-top-of my patchset.
> >
> > If you're interested, it should apply cleanly to the original
> > bio-cgroup, except for the get/put_cgroup_from_page() part.
> >
> > Thanks,
> > -Andrea
> > ---
> > bio-cgroup: encode bio_cgroup_id in page_cgroup->flags
> >
> > Encode the bio_cgroup_id into the flags argument of page_cgroup as
> > suggested by Kamezawa.
> >
> > Lower 16-bits of the flags attribute are used for the actual page_cgroup
> > flags. The rest is reserved to store the bio-cgroup id.
> >
> > This allows to save 4 bytes (in 32-bit architectures) or 8 bytes (in
> > 64-bit) for each page_cgroup element.
> >
> > Signed-off-by: Andrea Righi <righi.andrea@...il.com>
> > ---
> > include/linux/biotrack.h | 2 +-
> > include/linux/page_cgroup.h | 24 +++++++++++++++++++++---
> > mm/biotrack.c | 26 ++++++++++++--------------
> > 3 files changed, 34 insertions(+), 18 deletions(-)
> >
> > diff --git a/include/linux/biotrack.h b/include/linux/biotrack.h
> > index 25b8810..4bd0242 100644
> > --- a/include/linux/biotrack.h
> > +++ b/include/linux/biotrack.h
> > @@ -28,7 +28,7 @@ struct bio_cgroup {
> >
> > static inline void __init_bio_page_cgroup(struct page_cgroup *pc)
> > {
> > - pc->bio_cgroup_id = 0;
> > + page_cgroup_set_bio_id(pc, 0);
> > }
> >
> > extern struct cgroup *get_cgroup_from_page(struct page *page);
> > diff --git a/include/linux/page_cgroup.h b/include/linux/page_cgroup.h
> > index 00a49c5..af780a4 100644
> > --- a/include/linux/page_cgroup.h
> > +++ b/include/linux/page_cgroup.h
> > @@ -16,12 +16,30 @@ struct page_cgroup {
> > #ifdef CONFIG_CGROUP_MEM_RES_CTLR
> > struct mem_cgroup *mem_cgroup;
> > #endif
> > -#ifdef CONFIG_CGROUP_BIO
> > - int bio_cgroup_id;
> > -#endif
> > struct list_head lru; /* per cgroup LRU list */
> > };
> >
> > +#ifdef CONFIG_CGROUP_BIO
> > +/*
> > + * use lower 16 bits for flags and reserve the rest for the bio-cgroup id
> > + */
> > +#define BIO_CGROUP_ID_SHIFT (16)
> > +#define BIO_CGROUP_ID_BITS (8 * sizeof(unsigned long) - BIO_CGROUP_ID_SHIFT)
> > +
> > +static inline unsigned long page_cgroup_get_bio_id(struct page_cgroup *pc)
> > +{
> > + return pc->flags >> BIO_CGROUP_ID_SHIFT;
> > +}
> > +
> > +static inline void page_cgroup_set_bio_id(struct page_cgroup *pc,
> > + unsigned long id)
> > +{
> > + WARN_ON(id >= (1UL << BIO_CGROUP_ID_BITS));
> > + pc->flags &= (1UL << BIO_CGROUP_ID_SHIFT) - 1;
> > + pc->flags |= (unsigned long)(id << BIO_CGROUP_ID_SHIFT);
> > +}
> > +#endif
> > +
> Ah, there is "Lock" bit in pc->flags and above "set" code does read-modify-write
> without lock_page_cgroup().
>
> Could you use lock_page_cgroup() or cmpxchg ? (or using something magical technique ?)
If I'm not wrong this should guarantee atomicity without using
lock_page_cgroup().
Thanks,
-Andrea
---
bio-cgroup: encode bio_cgroup_id in page_cgroup->flags
Encode the bio_cgroup_id into the flags argument of page_cgroup as
suggested by Kamezawa.
Lower 16 bits (in 32-bit archs) or lower 32 bits (in 64-bit archs) of
the flags attribute are used for the actual page_cgroup flags. The upper
bits are reserved to store the bio-cgroup id.
This allows to save 4 bytes (in 32-bit architectures) or 8 bytes (in
64-bit) for each page_cgroup element.
Signed-off-by: Andrea Righi <righi.andrea@...il.com>
---
include/linux/page_cgroup.h | 42 +++++++++++++++++++++++++++++++++++++-----
mm/biotrack.c | 24 +++++++++++-------------
2 files changed, 48 insertions(+), 18 deletions(-)
diff --git a/include/linux/page_cgroup.h b/include/linux/page_cgroup.h
index a7249bb..864ad6f 100644
--- a/include/linux/page_cgroup.h
+++ b/include/linux/page_cgroup.h
@@ -16,14 +16,46 @@ struct page_cgroup {
#ifdef CONFIG_CGROUP_MEM_RES_CTLR
struct mem_cgroup *mem_cgroup;
#endif
-#ifdef CONFIG_CGROUP_BIO
- int bio_cgroup_id;
-#endif
-#if defined(CONFIG_CGROUP_MEM_RES_CTLR) || defined(CONFIG_CGROUP_BIO)
struct list_head lru; /* per cgroup LRU list */
-#endif
};
+#ifdef CONFIG_CGROUP_BIO
+/*
+ * Use the lower 16 bits (in 32-bit archs) or lower 32 bits (in 64-bit archs)
+ * of page_cgroup->flags for the actual flags and reserve the rest for the
+ * bio-cgroup id.
+ *
+ * This allows to atomically read and write the bio-cgroup id without using
+ * lock/unlock_page_cgroup().
+ */
+#if defined(CONFIG_64BIT)
+typedef uint32_t bio_cgroup_id_t;
+#elif defined(CONFIG_32BIT)
+typedef uint16_t bio_cgroup_id_t;
+#else
+#error "unsupported architecture"
+#endif
+
+#define BIO_CGROUP_ID_SHIFT (sizeof(bio_cgroup_id_t) * 8)
+#define BIO_CGROUP_ID_BITS (sizeof(bio_cgroup_id_t) * 8)
+#define BIO_CGROUP_ID_MASK ((1UL << BIO_CGROUP_ID_BITS) - 1)
+
+static inline unsigned long page_cgroup_get_bio_id(struct page_cgroup *pc)
+{
+ return (pc->flags >> BIO_CGROUP_ID_SHIFT) & BIO_CGROUP_ID_MASK;
+}
+
+static inline void page_cgroup_set_bio_id(struct page_cgroup *pc,
+ unsigned long id)
+{
+ bio_cgroup_id_t *ptr = (bio_cgroup_id_t *)((unsigned char *)&pc->flags +
+ (BIO_CGROUP_ID_SHIFT / 8));
+
+ WARN_ON(id >= (1UL << BIO_CGROUP_ID_BITS));
+ *ptr = (bio_cgroup_id_t)id;
+}
+#endif /* CONFIG_CGROUP_BIO */
+
void __meminit pgdat_page_cgroup_init(struct pglist_data *pgdat);
void __init page_cgroup_init(void);
struct page_cgroup *lookup_page_cgroup(struct page *page);
diff --git a/mm/biotrack.c b/mm/biotrack.c
index d3a35f1..01f83ba 100644
--- a/mm/biotrack.c
+++ b/mm/biotrack.c
@@ -80,7 +80,7 @@ void bio_cgroup_set_owner(struct page *page, struct mm_struct *mm)
if (unlikely(!pc))
return;
- pc->bio_cgroup_id = 0; /* 0: default bio_cgroup id */
+ __init_bio_page_cgroup(pc);
if (!mm)
return;
/*
@@ -93,11 +93,11 @@ void bio_cgroup_set_owner(struct page *page, struct mm_struct *mm)
goto out;
/*
* css_get(&bio->css) isn't called to increment the reference
- * count of this bio_cgroup "biog" so pc->bio_cgroup_id might turn
- * invalid even if this page is still active.
- * This approach is chosen to minimize the overhead.
+ * count of this bio_cgroup "biog" so the bio-cgroup id might turn
+ * invalid even if this page is still active. This approach is chosen
+ * to minimize the overhead.
*/
- pc->bio_cgroup_id = biog->id;
+ page_cgroup_set_bio_id(pc, biog->id);
out:
rcu_read_unlock();
}
@@ -110,7 +110,7 @@ void bio_cgroup_reset_owner(struct page *page, struct mm_struct *mm)
/*
* A little trick:
* Just call bio_cgroup_set_owner() for pages which are already
- * active since the bio_cgroup_id member of page_cgroup can be
+ * active since the bio-cgroup id member of page_cgroup can be
* updated without any locks. This is because an integer type of
* variable can be set a new value at once on modern cpus.
*/
@@ -146,12 +146,10 @@ void bio_cgroup_copy_owner(struct page *npage, struct page *opage)
opc = lookup_page_cgroup(opage);
if (unlikely(!opc))
return;
-
/*
- * Do this without any locks. The reason is the same as
- * bio_cgroup_reset_owner().
+ * XXX: is it safe to do this without locking?
*/
- npc->bio_cgroup_id = opc->bio_cgroup_id;
+ page_cgroup_set_bio_id(npc, page_cgroup_get_bio_id(opc));
}
/* Create a new bio-cgroup. */
@@ -248,7 +246,7 @@ struct cgroup *get_cgroup_from_page(struct page *page)
if (!pc)
return NULL;
lock_page_cgroup(pc);
- biog = find_bio_cgroup(pc->bio_cgroup_id);
+ biog = find_bio_cgroup(page_cgroup_get_bio_id(pc));
if (biog) {
css_get(&biog->css);
cgrp = biog->css.cgroup;
@@ -266,7 +264,7 @@ void put_cgroup_from_page(struct page *page)
if (!pc)
return;
lock_page_cgroup(pc);
- biog = find_bio_cgroup(pc->bio_cgroup_id);
+ biog = find_bio_cgroup(page_cgroup_get_bio_id(pc));
if (biog)
css_put(&biog->css);
unlock_page_cgroup(pc);
@@ -281,7 +279,7 @@ int get_bio_cgroup_id(struct bio *bio)
pc = lookup_page_cgroup(page);
if (pc)
- id = pc->bio_cgroup_id;
+ id = page_cgroup_get_bio_id(pc);
return id;
}
EXPORT_SYMBOL(get_bio_cgroup_id);
--
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