linux-kernel - Re: [PATCH 3/3] dcache: account external names as indirectly reclaimable memory

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Date:   Fri, 13 Apr 2018 16:20:00 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Michal Hocko <mhocko@...nel.org>, Minchan Kim <minchan@...nel.org>
Cc:     Roman Gushchin <guro@...com>, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Johannes Weiner <hannes@...xchg.org>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-team@...com
Subject: Re: [PATCH 3/3] dcache: account external names as indirectly
 reclaimable memory

On 04/13/2018 03:59 PM, Michal Hocko wrote:
> On Fri 13-04-18 22:35:19, Minchan Kim wrote:
>> On Mon, Mar 05, 2018 at 01:37:43PM +0000, Roman Gushchin wrote:
> [...]
>>> @@ -1614,9 +1623,11 @@ struct dentry *__d_alloc(struct super_block *sb, const struct qstr *name)
>>>  		name = &slash_name;
>>>  		dname = dentry->d_iname;
>>>  	} else if (name->len > DNAME_INLINE_LEN-1) {
>>> -		size_t size = offsetof(struct external_name, name[1]);
>>> -		struct external_name *p = kmalloc(size + name->len,
>>> -						  GFP_KERNEL_ACCOUNT);
>>> +		struct external_name *p;
>>> +
>>> +		reclaimable = offsetof(struct external_name, name[1]) +
>>> +			name->len;
>>> +		p = kmalloc(reclaimable, GFP_KERNEL_ACCOUNT);
>>
>> Can't we use kmem_cache_alloc with own cache created with SLAB_RECLAIM_ACCOUNT
>> if they are reclaimable? 
> 
> No, because names have different sizes and so we would basically have to
> duplicate many caches.

We would need kmalloc-reclaimable-X variants. It could be worth it,
especially if we find more similar usages. I suspect they would be more
useful than the existing dma-kmalloc-X :)

Maybe create both (dma and reclaimable) on demand?