linux-kernel - Re: [PATCH 4/4] mtd: nand: nandsim: convert to memalloc_noreclaim

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Date:   Wed, 5 Apr 2017 13:31:57 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Mel Gorman <mgorman@...hsingularity.net>,
        Johannes Weiner <hannes@...xchg.org>,
        linux-block@...r.kernel.org, nbd-general@...ts.sourceforge.net,
        open-iscsi@...glegroups.com, linux-scsi@...r.kernel.org,
        netdev@...r.kernel.org,
        Boris Brezillon <boris.brezillon@...e-electrons.com>,
        Richard Weinberger <richard@....at>
Subject: Re: [PATCH 4/4] mtd: nand: nandsim: convert to memalloc_noreclaim_*()

On Wed 05-04-17 09:47:00, Vlastimil Babka wrote:
> Nandsim has own functions set_memalloc() and clear_memalloc() for robust
> setting and clearing of PF_MEMALLOC. Replace them by the new generic helpers.
> No functional change.

This one smells like an abuser. Why the hell should read/write path
touch memory reserves at all!

> 
> Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
> Cc: Boris Brezillon <boris.brezillon@...e-electrons.com>
> Cc: Richard Weinberger <richard@....at>
> ---
>  drivers/mtd/nand/nandsim.c | 29 +++++++++--------------------
>  1 file changed, 9 insertions(+), 20 deletions(-)
> 
> diff --git a/drivers/mtd/nand/nandsim.c b/drivers/mtd/nand/nandsim.c
> index cef818f535ed..03a0d057bf2f 100644
> --- a/drivers/mtd/nand/nandsim.c
> +++ b/drivers/mtd/nand/nandsim.c
> @@ -40,6 +40,7 @@
>  #include <linux/list.h>
>  #include <linux/random.h>
>  #include <linux/sched.h>
> +#include <linux/sched/mm.h>
>  #include <linux/fs.h>
>  #include <linux/pagemap.h>
>  #include <linux/seq_file.h>
> @@ -1368,31 +1369,18 @@ static int get_pages(struct nandsim *ns, struct file *file, size_t count, loff_t
>  	return 0;
>  }
>  
> -static int set_memalloc(void)
> -{
> -	if (current->flags & PF_MEMALLOC)
> -		return 0;
> -	current->flags |= PF_MEMALLOC;
> -	return 1;
> -}
> -
> -static void clear_memalloc(int memalloc)
> -{
> -	if (memalloc)
> -		current->flags &= ~PF_MEMALLOC;
> -}
> -
>  static ssize_t read_file(struct nandsim *ns, struct file *file, void *buf, size_t count, loff_t pos)
>  {
>  	ssize_t tx;
> -	int err, memalloc;
> +	int err;
> +	unsigned int noreclaim_flag;
>  
>  	err = get_pages(ns, file, count, pos);
>  	if (err)
>  		return err;
> -	memalloc = set_memalloc();
> +	noreclaim_flag = memalloc_noreclaim_save();
>  	tx = kernel_read(file, pos, buf, count);
> -	clear_memalloc(memalloc);
> +	memalloc_noreclaim_restore(noreclaim_flag);
>  	put_pages(ns);
>  	return tx;
>  }
> @@ -1400,14 +1388,15 @@ static ssize_t read_file(struct nandsim *ns, struct file *file, void *buf, size_
>  static ssize_t write_file(struct nandsim *ns, struct file *file, void *buf, size_t count, loff_t pos)
>  {
>  	ssize_t tx;
> -	int err, memalloc;
> +	int err;
> +	unsigned int noreclaim_flag;
>  
>  	err = get_pages(ns, file, count, pos);
>  	if (err)
>  		return err;
> -	memalloc = set_memalloc();
> +	noreclaim_flag = memalloc_noreclaim_save();
>  	tx = kernel_write(file, buf, count, pos);
> -	clear_memalloc(memalloc);
> +	memalloc_noreclaim_restore(noreclaim_flag);
>  	put_pages(ns);
>  	return tx;
>  }
> -- 
> 2.12.2

-- 
Michal Hocko
SUSE Labs