linux-kernel - Re: [PATCH 3/3] mm,page_owner: Filter out stacks by a threshold counter

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Message-ID: <YxF6P++FVKvIUiQq@localhost.localdomain>
Date:   Fri, 2 Sep 2022 05:36:31 +0200
From:   Oscar Salvador <osalvador@...e.de>
To:     Ammar Faizi <ammarfaizi2@...weeb.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux MM Mailing List <linux-mm@...ck.org>,
        Michal Hocko <mhocko@...e.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Eric Dumazet <edumazet@...gle.com>,
        Waiman Long <longman@...hat.com>,
        Suren Baghdasaryan <surenb@...gle.com>
Subject: Re: [PATCH 3/3] mm,page_owner: Filter out stacks by a threshold
 counter

On Thu, Sep 01, 2022 at 03:31:51PM +0700, Ammar Faizi wrote:
> On 9/1/22 11:42 AM, Oscar Salvador wrote:> +static ssize_t read_page_owner_threshold(struct file *file, char __user *buf,
> > +	kbuf = kmalloc(count, GFP_KERNEL);
> > +	if (!kbuf)
> > +		return ENOMEM;
> 
> Missing a negative sign, return -ENOMEM.

Will fix.

> > +static ssize_t write_page_owner_threshold(struct file *file, const char __user *buf,
> > +					  size_t count, loff_t *pos)
> > +{
> > +	char *kbuf;
> > +	int ret = 0;
> > +
> > +	count = min_t(size_t, count, PAGE_SIZE);
> > +	kbuf = kmalloc(count, GFP_KERNEL);
> 
> This looks overestimating to me. For unsigned long, on a 64-bit system
> has max val 18446744073709551615 (20 chars).
> 
> You can use stack a allocated local variable with length 21. No need
> to use kmalloc(). The same way with the read() op.

Probably could do that, but I'll go with Michal's option and will use
seq_file.

Thanks!


-- 
Oscar Salvador
SUSE Labs