On Mon, 9 Apr 2018 10:03:45 +0200 Greg KH <[email protected]> wrote:
> On Mon, Apr 09, 2018 at 02:54:35PM +0900, Minchan Kim wrote: > > zRam as swap is useful for small memory device. However, swap means > > those pages on zram are mostly cold pages due to VM's LRU algorithm. > > Especially, once init data for application are touched for launching, > > they tend to be not accessed any more and finally swapped out. > > zRAM can store such cold pages as compressed form but it's pointless > > to keep in memory. Better idea is app developers free them directly > > rather than remaining them on heap. > > > > This patch tell us last access time of each block of zram via > > "cat /sys/kernel/debug/zram/zram0/block_state". > > > > The output is as follows, > > 300 75.033841 .wh > > 301 63.806904 s.. > > 302 63.806919 ..h > > > > First column is zram's block index and 3rh one represents symbol > > (s: same page w: written page to backing store h: huge page) of the > > block state. Second column represents usec time unit of the block > > was last accessed. So above example means the 300th block is accessed > > at 75.033851 second and it was huge so it was written to the backing > > store. > > > > Admin can leverage this information to catch cold|incompressible pages > > of process with *pagemap* once part of heaps are swapped out. > > > > Cc: Greg KH <[email protected]> > > Signed-off-by: Minchan Kim <[email protected]> > > --- > > Documentation/blockdev/zram.txt | 24 ++++++ > > drivers/block/zram/Kconfig | 9 +++ > > drivers/block/zram/zram_drv.c | 139 +++++++++++++++++++++++++++++--- > > drivers/block/zram/zram_drv.h | 5 ++ > > 4 files changed, 166 insertions(+), 11 deletions(-) > > > > diff --git a/Documentation/blockdev/zram.txt > > b/Documentation/blockdev/zram.txt > > index 78db38d02bc9..45509c7d5716 100644 > > --- a/Documentation/blockdev/zram.txt > > +++ b/Documentation/blockdev/zram.txt > > @@ -243,5 +243,29 @@ to backing storage rather than keeping it in memory. > > User should set up backing device via /sys/block/zramX/backing_dev > > before disksize setting. > > > > += memory tracking > > + > > +With CONFIG_ZRAM_MEMORY_TRACKING, user can know information of the > > +zram block. It could be useful to catch cold or incompressible > > +pages of the proess with*pagemap. > > +If you enable the feature, you could see block state via > > +/sys/kernel/debug/zram/zram0/block_state". The output is as follows, > > + > > + 300 75.033841 .wh > > + 301 63.806904 s.. > > + 302 63.806919 ..h > > + > > +First column is zram's block index. > > +Second column is access time. > > +Third column is state of the block. > > +(s: same page > > +w: written page to backing store > > +h: huge page) > > + > > +First line of above example says 300th block is accessed at 75.033841sec > > +and the block's state is huge so it is written back to the backing > > +storage. It's a debugging feature so anyone shouldn't rely on it to work > > +properly. > > + > > Nitin Gupta > > [email protected] > > diff --git a/drivers/block/zram/Kconfig b/drivers/block/zram/Kconfig > > index ac3a31d433b2..efe60c82d8ec 100644 > > --- a/drivers/block/zram/Kconfig > > +++ b/drivers/block/zram/Kconfig > > @@ -26,3 +26,12 @@ config ZRAM_WRITEBACK > > /sys/block/zramX/backing_dev. > > > > See zram.txt for more infomration. > > + > > +config ZRAM_MEMORY_TRACKING > > + bool "Tracking zram block status" > > + depends on ZRAM > > + select DEBUG_FS > > Select? Shouldn't you depend on this instead? Selecting is a pain to > try to track down what is keeping an option enabled. Okay, I will modify. > > > + help > > + With this feature, admin can track the state of allocated block > > + of zRAM. Admin could see the information via > > + /sys/kernel/debug/zram/zramX/block_state. > > A short note here as to where to find the documentation for what that > info is (i.e. in the file you wrote above?) Yub. Will change. > > > +#else > > +static void zram_debugfs_create(void) {}; > > +static void zram_debugfs_destroy(void) {}; > > +static void zram_accessed(struct zram *zram, u32 index) {}; > > +static void zram_reset_access(struct zram *zram, u32 index) {}; > > +static void zram_debugfs_register(struct zram *zram) {}; > > +static void zram_debugfs_unregister(struct zram *zram) {}; > > +#endif > > Much nicer, thanks! > > The above was only very minor nits, no need to change anything if you > don't want to. > > Acked-by: Greg Kroah-Hartman <[email protected]> I will wait a few days for getting review from Sergey and resend it with fix. Thanks for the review, Greg.
