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Message-ID: <517ABCF6.5040103@parallels.com>
Date: Fri, 26 Apr 2013 21:44:22 +0400
From: "Maxim V. Patlasov" <mpatlasov@...allels.com>
To: Miklos Szeredi <miklos@...redi.hu>
CC: Kirill Korotaev <dev@...allels.com>,
Pavel Emelianov <xemul@...allels.com>,
"fuse-devel@...ts.sourceforge.net" <fuse-devel@...ts.sourceforge.net>,
Kernel Mailing List <linux-kernel@...r.kernel.org>,
James Bottomley <jbottomley@...allels.com>,
Al Viro <viro@...iv.linux.org.uk>,
Linux-Fsdevel <linux-fsdevel@...r.kernel.org>,
<devel@...nvz.org>, Andrew Morton <akpm@...ux-foundation.org>,
<fengguang.wu@...el.com>, <mgorman@...e.de>, <riel@...hat.com>,
<hughd@...gle.com>, <gthelen@...gle.com>, <linux-mm@...ck.org>
Subject: Re: [fuse-devel] [PATCH 14/14] mm: Account for WRITEBACK_TEMP in
balance_dirty_pages
Miklos, MM folks,
04/26/2013 06:02 PM, Miklos Szeredi пишет:
> On Fri, Apr 26, 2013 at 12:32:24PM +0400, Maxim V. Patlasov wrote:
>
>>> The idea is that fuse filesystems should not go over the bdi limit even if
>>> the global limit hasn't been reached.
>> This might work, but kicking flusher every time someone write to
>> fuse mount and dives into balance_dirty_pages looks fishy.
> Yeah. Fixed patch attached.
The patch didn't work for me. I'll investigate what's wrong and get back
to you later.
>
>> Let's combine
>> our suggestions: mark fuse inodes with AS_FUSE_WRITEBACK flag and
>> convert what you strongly dislike above to:
>>
>> if (test_bit(AS_FUSE_WRITEBACK, &mapping->flags))
>> nr_dirty += global_page_state(NR_WRITEBACK_TEMP);
> I don't think this is right. The fuse daemon could itself be writing to another
> fuse filesystem, in which case blocking because of NR_WRITEBACK_TEMP being high
> isn't a smart strategy.
Please don't say 'blocking'. Per-bdi checks will decide whether to block
or not. In the case you set forth, judging on per-bdi checks would be
completely fine for upper fuse: it may and should block for a while if
lower fuse doesn't catch up.
>
> Furthermore it isn't enough. Becuase the root problem, I think, is that we
> allow fuse filesystems to grow a large number of dirty pages before throttling.
> This was never intended and it may actually have worked properly at a point in
> time but broke by some change to the dirty throttling algorithm.
Could someone from mm list step in and comment on this point? Which
approach is better to follow: account NR_WRITEBACK_TEMP in
balance_dirty_pages accurately (as we discussed in LSF/MM) or re-work
balance_dirty_pages in direction suggested by Miklos (fuse should never
go over the bdi limit even if the global limit hasn't been reached)?
I'm for accounting NR_WRITEBACK_TEMP because balance_dirty_pages is
already overcomplicated (imho) and adding new clauses for FUSE makes me
sick.
Thanks,
Maxim
>
> Thanks,
> Miklos
>
>
> diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
> index 137185c..195ee45 100644
> --- a/fs/fuse/inode.c
> +++ b/fs/fuse/inode.c
> @@ -291,6 +291,7 @@ struct inode *fuse_iget(struct super_block *sb, u64 nodeid,
> inode->i_flags |= S_NOATIME|S_NOCMTIME;
> inode->i_generation = generation;
> inode->i_data.backing_dev_info = &fc->bdi;
> + set_bit(AS_STRICTLIMIT, &inode->i_data.flags);
> fuse_init_inode(inode, attr);
> unlock_new_inode(inode);
> } else if ((inode->i_mode ^ attr->mode) & S_IFMT) {
> diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
> index 0e38e13..97f6a0c 100644
> --- a/include/linux/pagemap.h
> +++ b/include/linux/pagemap.h
> @@ -25,6 +25,7 @@ enum mapping_flags {
> AS_MM_ALL_LOCKS = __GFP_BITS_SHIFT + 2, /* under mm_take_all_locks() */
> AS_UNEVICTABLE = __GFP_BITS_SHIFT + 3, /* e.g., ramdisk, SHM_LOCK */
> AS_BALLOON_MAP = __GFP_BITS_SHIFT + 4, /* balloon page special map */
> + AS_STRICTLIMIT = __GFP_BITS_SHIFT + 5, /* strict dirty limit */
> };
>
> static inline void mapping_set_error(struct address_space *mapping, int error)
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index efe6814..b6db421 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -1226,6 +1226,7 @@ static void balance_dirty_pages(struct address_space *mapping,
> unsigned long dirty_ratelimit;
> unsigned long pos_ratio;
> struct backing_dev_info *bdi = mapping->backing_dev_info;
> + int strictlimit = test_bit(AS_STRICTLIMIT, &mapping->flags);
> unsigned long start_time = jiffies;
>
> for (;;) {
> @@ -1250,7 +1251,7 @@ static void balance_dirty_pages(struct address_space *mapping,
> */
> freerun = dirty_freerun_ceiling(dirty_thresh,
> background_thresh);
> - if (nr_dirty <= freerun) {
> + if (nr_dirty <= freerun && !strictlimit) {
> current->dirty_paused_when = now;
> current->nr_dirtied = 0;
> current->nr_dirtied_pause =
> @@ -1258,7 +1259,7 @@ static void balance_dirty_pages(struct address_space *mapping,
> break;
> }
>
> - if (unlikely(!writeback_in_progress(bdi)))
> + if (unlikely(!writeback_in_progress(bdi)) && !strictlimit)
> bdi_start_background_writeback(bdi);
>
> /*
> @@ -1296,8 +1297,12 @@ static void balance_dirty_pages(struct address_space *mapping,
> bdi_stat(bdi, BDI_WRITEBACK);
> }
>
> + if (unlikely(!writeback_in_progress(bdi)) &&
> + bdi_dirty > bdi_thresh / 2)
> + bdi_start_background_writeback(bdi);
> +
> dirty_exceeded = (bdi_dirty > bdi_thresh) &&
> - (nr_dirty > dirty_thresh);
> + ((nr_dirty > dirty_thresh) || strictlimit);
> if (dirty_exceeded && !bdi->dirty_exceeded)
> bdi->dirty_exceeded = 1;
>
>
>
--
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