linux-kernel - Re: [PATCH 3/3] f2fs: refactor flush_nat_entries to remove costly reorganizing ops

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Message-ID: <54392C79.4010607@oracle.com>
Date:	Sat, 11 Oct 2014 09:11:21 -0400
From:	Sasha Levin <sasha.levin@...cle.com>
To:	Jaegeuk Kim <jaegeuk@...nel.org>, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org,
	linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [PATCH 3/3] f2fs: refactor flush_nat_entries to remove costly
 reorganizing ops

On 09/23/2014 12:53 AM, Jaegeuk Kim wrote:
> +static void __set_nat_cache_dirty(struct f2fs_nm_info *nm_i,
> +						struct nat_entry *ne)
> +{
> +	nid_t set = ne->ni.nid / NAT_ENTRY_PER_BLOCK;
> +	struct nat_entry_set *head;
> +
> +	if (get_nat_flag(ne, IS_DIRTY))
> +		return;
> +retry:
> +	head = radix_tree_lookup(&nm_i->nat_set_root, set);
> +	if (!head) {
> +		head = f2fs_kmem_cache_alloc(nat_entry_set_slab, GFP_ATOMIC);

This is funny, you call f2fs_kmem_cache_alloc() here with GFP_ATOMIC because
of disabled preemption, but f2fs_kmem_cache_alloc() will attempt to
cond_resched() in case of failed allocations:

	retry:
	        entry = kmem_cache_alloc(cachep, flags);
	        if (!entry) {
	                cond_resched();
	                goto retry;
	        }

So in reality, f2fs_kmem_cache_alloc can't really work with GFP_ATOMIC,
and right now there are two different locations that call it with that
flag.


Thanks,
Sasha
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