From: Minchan Kim <minchan@kernel.org>
To: Dave Hansen <dave@sr71.net>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
akpm@linux-foundation.org, mgorman@suse.de,
tim.c.chen@linux.intel.com
Subject: Re: [v4][PATCH 1/6] mm: swap: defer clearing of page_private() for swap cache pages
Date: Tue, 4 Jun 2013 13:41:39 +0900 [thread overview]
Message-ID: <20130604044139.GB14719@blaptop> (raw)
In-Reply-To: <51ACADCD.70904@sr71.net>
On Mon, Jun 03, 2013 at 07:53:01AM -0700, Dave Hansen wrote:
> On 06/02/2013 10:40 PM, Minchan Kim wrote:
> >> > diff -puN mm/vmscan.c~__delete_from_swap_cache-dont-clear-page-private mm/vmscan.c
> >> > --- linux.git/mm/vmscan.c~__delete_from_swap_cache-dont-clear-page-private 2013-05-30 16:07:50.632079492 -0700
> >> > +++ linux.git-davehans/mm/vmscan.c 2013-05-30 16:07:50.637079712 -0700
> >> > @@ -494,6 +494,8 @@ static int __remove_mapping(struct addre
> >> > __delete_from_swap_cache(page);
> >> > spin_unlock_irq(&mapping->tree_lock);
> >> > swapcache_free(swap, page);
> >> > + set_page_private(page, 0);
> >> > + ClearPageSwapCache(page);
> > It it worth to support non-atomic version of ClearPageSwapCache?
>
> Just for this, probably not.
>
> It does look like a site where it would be theoretically safe to use
> non-atomic flag operations since the page is on a one-way trip to the
> allocator at this point and the __clear_page_locked() now happens _just_
> after this code.
True.
>
> But, personally, I'm happy to leave it as-is. The atomic vs. non-atomic
> flags look to me like a micro-optimization that we should use when we
> _know_ there will be some tangible benefit. Otherwise, they're just
> something extra for developers to trip over and cause very subtle bugs.
I just asked it because when I read the description of patchset, I felt
you were very sensitive to the atomic operation on many CPU system with
several sockets. Anyway, if you don't want it, I don't mind it, either.
--
Kind regards,
Minchan Kim
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WARNING: multiple messages have this Message-ID (diff)
From: Minchan Kim <minchan@kernel.org>
To: Dave Hansen <dave@sr71.net>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
akpm@linux-foundation.org, mgorman@suse.de,
tim.c.chen@linux.intel.com
Subject: Re: [v4][PATCH 1/6] mm: swap: defer clearing of page_private() for swap cache pages
Date: Tue, 4 Jun 2013 13:41:39 +0900 [thread overview]
Message-ID: <20130604044139.GB14719@blaptop> (raw)
In-Reply-To: <51ACADCD.70904@sr71.net>
On Mon, Jun 03, 2013 at 07:53:01AM -0700, Dave Hansen wrote:
> On 06/02/2013 10:40 PM, Minchan Kim wrote:
> >> > diff -puN mm/vmscan.c~__delete_from_swap_cache-dont-clear-page-private mm/vmscan.c
> >> > --- linux.git/mm/vmscan.c~__delete_from_swap_cache-dont-clear-page-private 2013-05-30 16:07:50.632079492 -0700
> >> > +++ linux.git-davehans/mm/vmscan.c 2013-05-30 16:07:50.637079712 -0700
> >> > @@ -494,6 +494,8 @@ static int __remove_mapping(struct addre
> >> > __delete_from_swap_cache(page);
> >> > spin_unlock_irq(&mapping->tree_lock);
> >> > swapcache_free(swap, page);
> >> > + set_page_private(page, 0);
> >> > + ClearPageSwapCache(page);
> > It it worth to support non-atomic version of ClearPageSwapCache?
>
> Just for this, probably not.
>
> It does look like a site where it would be theoretically safe to use
> non-atomic flag operations since the page is on a one-way trip to the
> allocator at this point and the __clear_page_locked() now happens _just_
> after this code.
True.
>
> But, personally, I'm happy to leave it as-is. The atomic vs. non-atomic
> flags look to me like a micro-optimization that we should use when we
> _know_ there will be some tangible benefit. Otherwise, they're just
> something extra for developers to trip over and cause very subtle bugs.
I just asked it because when I read the description of patchset, I felt
you were very sensitive to the atomic operation on many CPU system with
several sockets. Anyway, if you don't want it, I don't mind it, either.
--
Kind regards,
Minchan Kim
next prev parent reply other threads:[~2013-06-04 4:41 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-05-31 18:38 [v4][PATCH 0/6] mm: vmscan: Batch page reclamation under shink_page_list Dave Hansen
2013-05-31 18:38 ` Dave Hansen
2013-05-31 18:38 ` [v4][PATCH 1/6] mm: swap: defer clearing of page_private() for swap cache pages Dave Hansen
2013-05-31 18:38 ` Dave Hansen
2013-06-03 5:40 ` Minchan Kim
2013-06-03 5:40 ` Minchan Kim
2013-06-03 14:53 ` Dave Hansen
2013-06-03 14:53 ` Dave Hansen
2013-06-04 4:41 ` Minchan Kim [this message]
2013-06-04 4:41 ` Minchan Kim
2013-05-31 18:38 ` [v4][PATCH 2/6] mm: swap: make 'struct page' and swp_entry_t variants of swapcache_free() Dave Hansen
2013-05-31 18:38 ` Dave Hansen
2013-06-03 6:13 ` Minchan Kim
2013-06-03 6:13 ` Minchan Kim
2013-06-03 15:55 ` Dave Hansen
2013-06-03 15:55 ` Dave Hansen
2013-05-31 18:38 ` [v4][PATCH 3/6] mm: vmscan: break up __remove_mapping() Dave Hansen
2013-05-31 18:38 ` Dave Hansen
2013-06-03 8:28 ` Minchan Kim
2013-06-03 8:28 ` Minchan Kim
2013-05-31 18:39 ` [v4][PATCH 4/6] mm: vmscan: break out mapping "freepage" code Dave Hansen
2013-05-31 18:39 ` Dave Hansen
2013-06-03 8:35 ` Minchan Kim
2013-06-03 8:35 ` Minchan Kim
2013-05-31 18:39 ` [v4][PATCH 5/6] mm: vmscan: batch shrink_page_list() locking operations Dave Hansen
2013-05-31 18:39 ` Dave Hansen
2013-05-31 18:39 ` [v4][PATCH 6/6] mm: vmscan: drain batch list during long operations Dave Hansen
2013-05-31 18:39 ` Dave Hansen
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