Hi Minchan, > -----Original Message----- > From: Minchan Kim [mailto:minchan@xxxxxxxxxx] > Sent: Monday, August 25, 2014 8:36 AM > To: Chao Yu > Cc: linux-kernel@xxxxxxxxxxxxxxx; linux-mm@xxxxxxxxx; ngupta@xxxxxxxxxx; 'Jerome Marchand'; > 'Sergey Senozhatsky'; 'Andrew Morton' > Subject: Re: [PATCH v3] zram: add num_discards for discarded pages stat > > Hello Chao, > > On Fri, Aug 22, 2014 at 04:21:01PM +0800, Chao Yu wrote: > > Since we have supported handling discard request in this commit > > f4659d8e620d08bd1a84a8aec5d2f5294a242764 (zram: support REQ_DISCARD), zram got > > one more chance to free unused memory whenever received discard request. But > > without stating for discard request, there is no method for user to know whether > > discard request has been handled by zram or how many blocks were discarded by > > zram when user wants to know the effect of discard. > > My concern is that how much we are able to know the effect of discard > exactly with your patch. > > The issue I can think of is zram-swap discard. > Now, zram handles notification from VM to free duplicated copy between > VM-owned memory and zRAM-owned's one so discarding for zram-swap might > be pointless overhead but your stat indicates lots of free page discarded > without real freeing so that user might think "We should keep enable > swap discard for zRAM because the stat indicates it's really good". Agreed. > > In summary, wouldn't it better to have two? Yeah, I'd like to. > > num_discards, > num_failed_discards? It's good, but, IMHO, as it's not failed to discard pages due to inside error of zRAM, How about show this information more positive by using: num_discard_req, num_discarded Then user might think "We can keep on using real-time mode or batch mode discard, because our freed pages are increased continuously shew by the num_discarded with sending discard reqs each time. How do you think? Thanks, Yu > > For it, we should modify zram_free_page has return value. > What do other guys think? > > > > > In this patch, we add num_discards to stat discarded pages, and export it to > > sysfs for users. > > > > * From v1 > > * Update zram document to show num_discards in statistics list. > > > > * From v2 > > * Update description of this patch with clear goal. > > > > Signed-off-by: Chao Yu <chao2.yu@xxxxxxxxxxx> > > --- > > Documentation/ABI/testing/sysfs-block-zram | 10 ++++++++++ > > Documentation/blockdev/zram.txt | 1 + > > drivers/block/zram/zram_drv.c | 3 +++ > > drivers/block/zram/zram_drv.h | 1 + > > 4 files changed, 15 insertions(+) > > > > diff --git a/Documentation/ABI/testing/sysfs-block-zram > b/Documentation/ABI/testing/sysfs-block-zram > > index 70ec992..fa8936e 100644 > > --- a/Documentation/ABI/testing/sysfs-block-zram > > +++ b/Documentation/ABI/testing/sysfs-block-zram > > @@ -57,6 +57,16 @@ Description: > > The failed_writes file is read-only and specifies the number of > > failed writes happened on this device. > > > > + > > +What: /sys/block/zram<id>/num_discards > > +Date: August 2014 > > +Contact: Chao Yu <chao2.yu@xxxxxxxxxxx> > > +Description: > > + The num_discards file is read-only and specifies the number of > > + physical blocks which are discarded by this device. These blocks > > + are included in discard request which is sended by filesystem as > > + the blocks are no longer used. > > + > > What: /sys/block/zram<id>/max_comp_streams > > Date: February 2014 > > Contact: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx> > > diff --git a/Documentation/blockdev/zram.txt b/Documentation/blockdev/zram.txt > > index 0595c3f..e50e18b 100644 > > --- a/Documentation/blockdev/zram.txt > > +++ b/Documentation/blockdev/zram.txt > > @@ -89,6 +89,7 @@ size of the disk when not in use so a huge zram is wasteful. > > num_writes > > failed_reads > > failed_writes > > + num_discards > > invalid_io > > notify_free > > zero_pages > > diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c > > index d00831c..904e7a5 100644 > > --- a/drivers/block/zram/zram_drv.c > > +++ b/drivers/block/zram/zram_drv.c > > @@ -606,6 +606,7 @@ static void zram_bio_discard(struct zram *zram, u32 index, > > bit_spin_lock(ZRAM_ACCESS, &meta->table[index].value); > > zram_free_page(zram, index); > > bit_spin_unlock(ZRAM_ACCESS, &meta->table[index].value); > > + atomic64_inc(&zram->stats.num_discards); > > index++; > > n -= PAGE_SIZE; > > } > > @@ -866,6 +867,7 @@ ZRAM_ATTR_RO(num_reads); > > ZRAM_ATTR_RO(num_writes); > > ZRAM_ATTR_RO(failed_reads); > > ZRAM_ATTR_RO(failed_writes); > > +ZRAM_ATTR_RO(num_discards); > > ZRAM_ATTR_RO(invalid_io); > > ZRAM_ATTR_RO(notify_free); > > ZRAM_ATTR_RO(zero_pages); > > @@ -879,6 +881,7 @@ static struct attribute *zram_disk_attrs[] = { > > &dev_attr_num_writes.attr, > > &dev_attr_failed_reads.attr, > > &dev_attr_failed_writes.attr, > > + &dev_attr_num_discards.attr, > > &dev_attr_invalid_io.attr, > > &dev_attr_notify_free.attr, > > &dev_attr_zero_pages.attr, > > diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h > > index e0f725c..2994aaf 100644 > > --- a/drivers/block/zram/zram_drv.h > > +++ b/drivers/block/zram/zram_drv.h > > @@ -86,6 +86,7 @@ struct zram_stats { > > atomic64_t num_writes; /* --do-- */ > > atomic64_t failed_reads; /* can happen when memory is too low */ > > atomic64_t failed_writes; /* can happen when memory is too low */ > > + atomic64_t num_discards; /* no. of discarded pages */ > > atomic64_t invalid_io; /* non-page-aligned I/O requests */ > > atomic64_t notify_free; /* no. of swap slot free notifications */ > > atomic64_t zero_pages; /* no. of zero filled pages */ > > -- > > 2.0.1.474.g72c7794 > > > > > > -- > > To unsubscribe, send a message with 'unsubscribe linux-mm' in > > the body to majordomo@xxxxxxxxx. For more info on Linux MM, > > see: http://www.linux-mm.org/ . > > Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a> > > -- > Kind regards, > Minchan Kim -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>