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Message-ID: <20140814125458.GA966@swordfish> Date: Thu, 14 Aug 2014 21:54:58 +0900 From: Sergey Senozhatsky <sergey.senozhatsky@...il.com> To: Minchan Kim <minchan@...nel.org> Cc: Sergey Senozhatsky <sergey.senozhatsky@...il.com>, Jerome Marchand <jmarchan@...hat.com>, Chao Yu <chao2.yu@...sung.com>, Nitin Gupta <ngupta@...are.org>, linux-kernel@...r.kernel.org Subject: Re: [PATCH v2] zram: fix incorrectly stat with failed_reads Hi, On (08/14/14 08:02), Minchan Kim wrote: > On Wed, Aug 13, 2014 at 11:43:04PM +0900, Sergey Senozhatsky wrote: > > 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 <jmarchan@...hat.com> > > > > To: Chao Yu <chao2.yu@...sung.com>, minchan@...nel.org > > > > CC: ngupta@...are.org, linux-kernel@...r.kernel.org, 'Sergey Senozhatsky' > > > > <sergey.senozhatsky@...il.com>, 'Andrew Morton' > > > > <akpm@...ux-foundation.org> > > > > 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 <chao2.yu@...sung.com> > > > > > > > > Acked-by: Jerome Marchand <jmarchan@...hat.com> > > > > > > Acked-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com> > > > > > > -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 */ > > How often does it happen? > I don't think it's valuable to maintain if it's too rare. > Rather, I'd like to remove the comment on failed_writes. :) > I don't think I've ever observed any errors. and, apparently, lzo is always `return LZO_E_OK'. so let's just drop it. -ss -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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