From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753217AbaHMOoR (ORCPT ); Wed, 13 Aug 2014 10:44:17 -0400 Received: from mail-pa0-f46.google.com ([209.85.220.46]:35174 "EHLO mail-pa0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753177AbaHMOoP (ORCPT ); Wed, 13 Aug 2014 10:44:15 -0400 Date: Wed, 13 Aug 2014 23:43:04 +0900 From: Sergey Senozhatsky To: Minchan Kim Cc: Jerome Marchand , Chao Yu , Nitin Gupta , linux-kernel@vger.kernel.org, Sergey Senozhatsky Subject: Re: [PATCH v2] zram: fix incorrectly stat with failed_reads Message-ID: <20140813144304.GB1091@swordfish> References: <009001cfb69a$a8470840$f8d518c0$@samsung.com> <53EB2271.1080002@redhat.com> <20140813113257.GA948@swordfish> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140813113257.GA948@swordfish> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, On (08/13/14 20:32), Sergey Senozhatsky wrote: > On (08/13/14 10:31), Jerome Marchand wrote: > > Date: Wed, 13 Aug 2014 10:31:45 +0200 > > From: Jerome Marchand > > To: Chao Yu , minchan@kernel.org > > CC: ngupta@vflare.org, linux-kernel@vger.kernel.org, 'Sergey Senozhatsky' > > , 'Andrew Morton' > > > > Subject: Re: [PATCH v2] zram: fix incorrectly stat with failed_reads > > User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 > > Thunderbird/24.6.0 > > > > On 08/13/2014 04:01 AM, Chao Yu wrote: > > > Since we allocate a temporary buffer in zram_bvec_read to handle partial page > > > operations in this commit 924bd88d703e53d30f393fac6117f8f1bc79aab6 (Staging: > > > zram: allow partial page operations), our ->failed_reads value may be incorrect > > > as we do not increase its value when failed to allocate the temporary buffer. > > > > > > Let's fix this issue and correct the annotation of failed_reads. > > > > > > v2: clean codes of failed_{reads,writes} stat pointed out by Minchan Kim, and > > > this cleanup also fix incorrectly stat when fail in zram_decompress_page. > > > > > > Signed-off-by: Chao Yu > > > > Acked-by: Jerome Marchand > > Acked-by: Sergey Senozhatsky > > -ss > > > > --- > > > drivers/block/zram/zram_drv.c | 10 +++++++--- > > > drivers/block/zram/zram_drv.h | 2 +- > > > 2 files changed, 8 insertions(+), 4 deletions(-) > > > > > > diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c > > > index dfa4024..d00831c 100644 > > > --- a/drivers/block/zram/zram_drv.c > > > +++ b/drivers/block/zram/zram_drv.c > > > @@ -378,7 +378,6 @@ static int zram_decompress_page(struct zram *zram, char *mem, u32 index) > > > /* Should NEVER happen. Return bio error if it does. */ > > > if (unlikely(ret)) { > > > pr_err("Decompression failed! err=%d, page=%u\n", ret, index); > > > - atomic64_inc(&zram->stats.failed_reads); > > > return ret; > > > } > > > > > > @@ -547,8 +546,6 @@ out: > > > zcomp_strm_release(zram->comp, zstrm); > > > if (is_partial_io(bvec)) > > > kfree(uncmem); > > > - if (ret) > > > - atomic64_inc(&zram->stats.failed_writes); > > > return ret; > > > } > > > > > > @@ -566,6 +563,13 @@ static int zram_bvec_rw(struct zram *zram, struct bio_vec *bvec, u32 index, > > > ret = zram_bvec_write(zram, bvec, index, offset); > > > } > > > > > > + if (unlikely(ret)) { > > > + if (rw == READ) > > > + atomic64_inc(&zram->stats.failed_reads); > > > + else > > > + atomic64_inc(&zram->stats.failed_writes); > > > + } > > > + > > > return ret; > > > } > > > > > > diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h > > > index 5b0afde..e0f725c 100644 > > > --- a/drivers/block/zram/zram_drv.h > > > +++ b/drivers/block/zram/zram_drv.h > > > @@ -84,7 +84,7 @@ struct zram_stats { > > > atomic64_t compr_data_size; /* compressed size of pages stored */ > > > atomic64_t num_reads; /* failed + successful */ > > > atomic64_t num_writes; /* --do-- */ > > > - atomic64_t failed_reads; /* should NEVER! happen */ > > > + atomic64_t failed_reads; /* can happen when memory is too low */ this grabbed my attention. "failed_writes; /* can happen when memory is too low */" theoretically, we can have a misbehaving compression algorithm. so the question is -- should we fail write() if compression has failed for any other reason, rather than -ENOMEM? alternatively, we can store uncompressed user mem, just the same way we do for `badly' compressed buffers, set a FAILED_COMPRESSION flag (so we will not leak kernel memory on read() if we failed to compress is_partial_io() bv_page), and on read() copy it out as is, just as we do for `badly' compessed pages. so, what do you think? /* I can take a look on it */ -ss > > > atomic64_t failed_writes; /* can happen when memory is too low */ > > > atomic64_t invalid_io; /* non-page-aligned I/O requests */ > > > atomic64_t notify_free; /* no. of swap slot free notifications */ > > > > > > > > >