linux-kernel - Re: [PATCH 2/2] zram: do not count duplicated pages as compressed

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Tue, 16 May 2017 10:59:19 +0900
From:   Minchan Kim <minchan@...nel.org>
To:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, Joonsoo Kim <iamjoonsoo.kim@....com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        kernel-team <kernel-team@....com>
Subject: Re: [PATCH 2/2] zram: do not count duplicated pages as compressed

Hi Sergey,

On Tue, May 16, 2017 at 10:30:22AM +0900, Sergey Senozhatsky wrote:
> On (05/15/17 16:41), Minchan Kim wrote:
> [..]
> > diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> > index b885356551e9..8152e405117b 100644
> > --- a/drivers/block/zram/zram_drv.c
> > +++ b/drivers/block/zram/zram_drv.c
> > @@ -624,15 +624,22 @@ static void zram_free_page(struct zram *zram, size_t index)
> >  		return;
> >  	}
> >  
> > +	if (zram_dedup_enabled(zram) &&
> > +			zram_test_flag(zram, index, ZRAM_DUP)) {
> > +		zram_clear_flag(zram, index, ZRAM_DUP);
> > +		atomic64_sub(entry->len, &zram->stats.dup_data_size);
> > +		goto out;
> > +	}
> 
> so that `goto' there is to just jump over ->stats.compr_data_size?

Yub.

> can you sub ->stats.compr_data_size before the `if' and avoid labels?


> 
> >  	if (!entry)
> >  		return;
> 
> shouldn't this `if' be moved before `if (zram_dedup_enabled(zram)`?

You mean this?

static void zram_free_page(..) {
        if (zram_test_flag(zram, index, ZRAM_SAME))
                ...

        if (!entry)
                return;

        if (zram_dedup_enabled(zram) && xxxx)) {
                zram_clear_flag(ZRAM_DUP);
                atomic64_sub(entry->len, &zram->stats.dup_data_size);
        } else {
                atomic64_sub(zram_get_obj_size(zram, index),
                                        &zram->stats.compr_dat_size);
        }

        zram_entry_free
        zram_set_entry
        zram_set_obj_size
}

> 
> 
> [..]
> > @@ -794,7 +801,15 @@ static int __zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index)
> >  	entry = zram_dedup_find(zram, page, &checksum);
> >  	if (entry) {
> >  		comp_len = entry->len;
> > -		goto found_dup;
> > +		zram_slot_lock(zram, index);
> > +		zram_free_page(zram, index);
> > +		zram_set_flag(zram, index, ZRAM_DUP);
> > +		zram_set_entry(zram, index, entry);
> > +		zram_set_obj_size(zram, index, comp_len);
> > +		zram_slot_unlock(zram, index);
> > +		atomic64_add(comp_len, &zram->stats.dup_data_size);
> > +		atomic64_inc(&zram->stats.pages_stored);
> > +		return 0;
> 
> hm. that's a somewhat big code duplication. isn't it?

Yub. 3 parts. above part,  zram_same_page_write and tail of __zram_bvec_write.

Do you have any idea? Feel free to suggest. :)
Thanks.