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Date: Thu, 12 Mar 2009 10:52:26 +0900
From: Minchan Kim <minchan.kim@...il.com>
To: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc: Minchan Kim <minchan.kim@...il.com>,
Andrew Morton <akpm@...ux-foundation.org>, dhowells@...hat.com,
torvalds@...ux-foundation.org, peterz@...radead.org,
Enrik.Berkhan@...com, uclinux-dev@...inux.org,
linux-kernel@...r.kernel.org, linux-mm@...ck.org,
Johannes Weiner <hannes@...xchg.org>,
Rik van Riel <riel@...riel.com>,
Lee Schermerhorn <lee.schermerhorn@...com>
Subject: Re: [PATCH] NOMMU: Pages allocated to a ramfs inode's pagecache may
get wrongly discarded
Hi, Kosaki-san.
I think ramfs pages's unevictablility should not depend on CONFIG_UNEVICTABLE_LRU.
It would be better to remove dependency of CONFIG_UNEVICTABLE_LRU ?
How about this ?
It's just RFC. It's not tested.
That's because we can't reclaim that pages regardless of whether there is unevictable list or not
>From 487ce9577ea9c43b04ff340a1ba8c4030873e875 Mon Sep 17 00:00:00 2001
From: MinChan Kim <minchan.kim@...il.com>
Date: Thu, 12 Mar 2009 10:35:37 +0900
Subject: [PATCH] test
Signed-off-by: MinChan Kim <minchan.kim@...il.com>
---
include/linux/pagemap.h | 9 ---------
include/linux/swap.h | 9 ++-------
2 files changed, 2 insertions(+), 16 deletions(-)
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 4d27bf8..0cf024c 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -32,7 +32,6 @@ static inline void mapping_set_error(struct address_space *mapping, int error)
}
}
-#ifdef CONFIG_UNEVICTABLE_LRU
#define AS_UNEVICTABLE (__GFP_BITS_SHIFT + 2) /* e.g., ramdisk, SHM_LOCK */
static inline void mapping_set_unevictable(struct address_space *mapping)
@@ -51,14 +50,6 @@ static inline int mapping_unevictable(struct address_space *mapping)
return test_bit(AS_UNEVICTABLE, &mapping->flags);
return !!mapping;
}
-#else
-static inline void mapping_set_unevictable(struct address_space *mapping) { }
-static inline void mapping_clear_unevictable(struct address_space *mapping) { }
-static inline int mapping_unevictable(struct address_space *mapping)
-{
- return 0;
-}
-#endif
static inline gfp_t mapping_gfp_mask(struct address_space * mapping)
{
diff --git a/include/linux/swap.h b/include/linux/swap.h
index a3af95b..18c639b 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -233,8 +233,9 @@ static inline int zone_reclaim(struct zone *z, gfp_t mask, unsigned int order)
}
#endif
-#ifdef CONFIG_UNEVICTABLE_LRU
extern int page_evictable(struct page *page, struct vm_area_struct *vma);
+
+#ifdef CONFIG_UNEVICTABLE_LRU
extern void scan_mapping_unevictable_pages(struct address_space *);
extern unsigned long scan_unevictable_pages;
@@ -243,12 +244,6 @@ extern int scan_unevictable_handler(struct ctl_table *, int, struct file *,
extern int scan_unevictable_register_node(struct node *node);
extern void scan_unevictable_unregister_node(struct node *node);
#else
-static inline int page_evictable(struct page *page,
- struct vm_area_struct *vma)
-{
- return 1;
-}
-
static inline void scan_mapping_unevictable_pages(struct address_space *mapping)
{
}
--
1.5.4.3
> On Thu, 12 Mar 2009 10:04:41 +0900 (JST)
> KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> wrote:
>
> Hi
>
> > >> Page reclaim shouldn't be even attempting to reclaim or write back
> > >> ramfs pagecache pages - reclaim can't possibly do anything with these
> > >> pages!
> > >>
> > >> Arguably those pages shouldn't be on the LRU at all, but we haven't
> > >> done that yet.
> > >>
> > >> Now, my problem is that I can't 100% be sure that we _ever_ implemented
> > >> this properly. ?I _think_ we did, in which case we later broke it. ?If
> > >> we've always been (stupidly) trying to pageout these pages then OK, I
> > >> guess your patch is a suitable 2.6.29 stopgap.
> > >
> > > OK, I can't find any code anywhere in which we excluded ramfs pages
> > > from consideration by page reclaim. ?How dumb.
> >
> > The ramfs considers it in just CONFIG_UNEVICTABLE_LRU case
> > It that case, ramfs_get_inode calls mapping_set_unevictable.
> > So, page reclaim can exclude ramfs pages by page_evictable.
> > It's problem .
>
> Currently, CONFIG_UNEVICTABLE_LRU can't use on nommu machine
> because nobody of vmscan folk havbe nommu machine.
>
> Yes, it is very stupid reason. _very_ welcome to tester! :)
>
>
>
> David, Could you please try following patch if you have NOMMU machine?
> it is straightforward porting to nommu.
>
>
> ==
> Subject: [PATCH] remove to depend on MMU from CONFIG_UNEVICTABLE_LRU
>
> logically, CONFIG_UNEVICTABLE_LRU doesn't depend on MMU.
> but current code does by mistake. fix it.
>
>
> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
> ---
> mm/Kconfig | 1 -
> mm/nommu.c | 24 ++++++++++++++++++++++++
> 2 files changed, 24 insertions(+), 1 deletion(-)
>
> Index: b/mm/Kconfig
> ===================================================================
> --- a/mm/Kconfig 2008-12-28 20:55:23.000000000 +0900
> +++ b/mm/Kconfig 2008-12-28 21:24:08.000000000 +0900
> @@ -212,7 +212,6 @@ config VIRT_TO_BUS
> config UNEVICTABLE_LRU
> bool "Add LRU list to track non-evictable pages"
> default y
> - depends on MMU
> help
> Keeps unevictable pages off of the active and inactive pageout
> lists, so kswapd will not waste CPU time or have its balancing
> Index: b/mm/nommu.c
> ===================================================================
> --- a/mm/nommu.c 2008-12-25 08:26:37.000000000 +0900
> +++ b/mm/nommu.c 2008-12-28 21:29:36.000000000 +0900
> @@ -1521,3 +1521,27 @@ int access_process_vm(struct task_struct
> mmput(mm);
> return len;
> }
> +
> +/*
> + * LRU accounting for clear_page_mlock()
> + */
> +void __clear_page_mlock(struct page *page)
> +{
> + VM_BUG_ON(!PageLocked(page));
> +
> + if (!page->mapping) { /* truncated ? */
> + return;
> + }
> +
> + dec_zone_page_state(page, NR_MLOCK);
> + count_vm_event(UNEVICTABLE_PGCLEARED);
> + if (!isolate_lru_page(page)) {
> + putback_lru_page(page);
> + } else {
> + /*
> + * We lost the race. the page already moved to evictable list.
> + */
> + if (PageUnevictable(page))
> + count_vm_event(UNEVICTABLE_PGSTRANDED);
> + }
> +}
>
>
>
>
--
Kinds Regards
Minchan Kim
--
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