From: Sergey Senozhatsky <email@example.com> To: Minchan Kim <firstname.lastname@example.org> Cc: Sergey Senozhatsky <email@example.com>, Andrew Morton <firstname.lastname@example.org>, email@example.com, Joonsoo Kim <firstname.lastname@example.org>, Sergey Senozhatsky <email@example.com>, kernel-team <firstname.lastname@example.org>, email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com Subject: Re: [PATCH 2/2] zram: do not count duplicated pages as compressed Date: Wed, 17 May 2017 18:14:23 +0900 [thread overview] Message-ID: <20170517091423.GA14662@jagdpanzerIV.localdomain> (raw) In-Reply-To: <20170517083212.GA25750@bbox> Hello Minchan, On (05/17/17 17:32), Minchan Kim wrote: [..] > > what we can return now is a `partially updated' data, with some new > > and some stale pages. this is quite unlikely to end up anywhere good. > > am I wrong? > > > > why does `rd block 4' in your case causes Oops? as a worst case scenario? > > application does not expect page to be 'all A' at this point. pages are > > likely to belong to some mappings/files/etc., and there is likely a data > > dependency between them, dunno C++ objects that span across pages or > > JPEG images, etc. so returning "new data new data stale data" is a bit > > fishy. > > I thought more about it and start to confuse. :/ sorry, I'm not sure I see what's the source of your confusion :) my point is - we should not let READ succeed if we know that WRITE failed. assume JPEG image example, over-write block 1 aaa->xxx OK over-write block 2 bbb->yyy OK over-write block 3 ccc->zzz error reading that JPEG file read block 1 xxx OK read block 2 yyy OK read block 3 ccc OK << we should not return OK here. because "xxxyyyccc" is not the correct JPEG file anyway. do you agree that telling application that read() succeeded and at the same returning corrupted "xxxyyyccc" instead of "xxxyyyzzz" is not correct? so how about this, - if we fail to compress page (S/W or H/W compressor error, depending on particular setup) let's store it uncompressed (page_size-d zspool object). ? this should do the trick. at least we will have correct data: xxx - compressed yyy - compressed zzz - uncompressed, because compressing back-end returned an error. thoughts? -ss
next prev parent reply other threads:[~2017-05-17 9:14 UTC|newest] Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top 2017-05-15 7:41 [PATCH 1/2] zram: count same page write as page_stored Minchan Kim 2017-05-15 7:41 ` [PATCH 2/2] zram: do not count duplicated pages as compressed Minchan Kim 2017-05-16 1:30 ` Sergey Senozhatsky 2017-05-16 1:59 ` Minchan Kim 2017-05-16 2:36 ` Sergey Senozhatsky 2017-05-16 5:26 ` Minchan Kim 2017-05-16 5:45 ` Sergey Senozhatsky 2017-05-16 7:16 ` Minchan Kim 2017-05-16 7:36 ` Sergey Senozhatsky 2017-05-17 8:32 ` Minchan Kim 2017-05-17 9:14 ` Sergey Senozhatsky [this message] 2017-05-18 4:53 ` Minchan Kim 2017-05-21 7:04 ` Christoph Hellwig 2017-05-21 7:15 ` Minchan Kim 2017-05-16 1:11 ` [PATCH 1/2] zram: count same page write as page_stored Sergey Senozhatsky
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