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Message-ID: <CAOH5QeCTmSBX+Ov=A7TLDWCLxNebpFOuNx+v-z0DwT-Y1umqzw@mail.gmail.com>
Date: Wed, 9 Jun 2021 22:58:00 +0800
From: yong w <yongw.pur@...il.com>
To: Greg KH <gregkh@...uxfoundation.org>
Cc: minchan@...nel.org, ngupta@...are.org, senozhatsky@...omium.org,
axboe@...nel.dk, akpm@...ux-foundation.org,
songmuchun@...edance.com, David Hildenbrand <david@...hat.com>,
linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
linux-mm@...ck.org, willy@...radead.org, linux-api@...r.kernel.org,
lu.zhongjun@....com.cn, yang.yang29@....com.cn,
zhang.wenya1@....com.cn, wang.yong12@....com.cn
Subject: Re: [RFC PATCH V3] zram:calculate available memory when zram is used
Greg KH <gregkh@...uxfoundation.org> 于2021年6月8日周二 下午5:28写道：
>
> On Mon, Jun 07, 2021 at 08:39:14AM -0700, yongw.pur@...il.com wrote:
> > From: wangyong <wang.yong12@....com.cn>
> >
> > When zram is used, available+Swap free memory is obviously bigger than we
> > actually can use, because zram can compress memory by compression
> > algorithm and zram compressed data will occupy memory too.
> >
> > So, we can count the compression ratio of zram in the kernel. The space
> > will be saved by zram and other swap device are calculated as follows:
> > zram[swapfree - swapfree * compress ratio] + swapdev[swapfree]
> > We can evaluate the available memory of the whole system as:
> > MemAvailable+zram[swapfree - swapfree * compress ratio]+swapdev[swapfree]
> >
> > Add an entry to the /proc/meminfo file, returns swap will save space.
> > Which name is more appropriate is still under consideration.
> > There are several alternative names: SwapAvailable, SwapSaved,
> > SwapCompressible, Which is better?
> >
> > Adding new entries has little effect on user program, since parsers
> > usually parse by keywords
> >
> > Changes from v2:
> > *Add interface description document
> > *Other mistakes and problems fix
> >
> > Changes from v1:
> > *Use a new interface to return memory savings when using swap devices
> > *Zram add min_compr_ratio attr
>
> These "Changes" need to go below the --- line please.
>
> >
> > Signed-off-by: wangyong <wang.yong12@....com.cn>
> > ---
> > Documentation/admin-guide/blockdev/zram.rst | 6 ++
> > Documentation/filesystems/proc.rst | 4 ++
> > drivers/block/zram/zcomp.h | 8 +++
> > drivers/block/zram/zram_drv.c | 19 ++++++
> > drivers/block/zram/zram_drv.h | 1 +
> > fs/proc/meminfo.c | 1 +
> > include/linux/swap.h | 11 ++++
> > mm/swapfile.c | 95 +++++++++++++++++++++++++++++
> > mm/vmscan.c | 1 +
> > 9 files changed, 146 insertions(+)
> >
> > diff --git a/Documentation/admin-guide/blockdev/zram.rst b/Documentation/admin-guide/blockdev/zram.rst
> > index 700329d..3b7c4c4 100644
> > --- a/Documentation/admin-guide/blockdev/zram.rst
> > +++ b/Documentation/admin-guide/blockdev/zram.rst
> > @@ -283,6 +283,12 @@ a single line of text and contains the following stats separated by whitespace:
> > Unit: 4K bytes
> > ============== =============================================================
> >
> > +File /sys/block/zram<id>/min_compr_ratio
> > +
> > +The min_compr_ratio file represents the min_compr_ratio during zram swapping out.The calculation formula is as follows:
> > +(orig_size * 100) / compr_data_size
> > +
> > +
>
>
> sysfs files need to be documented in Documentation/ABI/ files. You can
> reference them in other documentation files, but they need to be in the
> ABI/ directory as well.
>
> Also please wrap your lines at the proper length and use a ' ' after a
> '.'
OK, I'll be careful next time.
>
> > 9) Deactivate
> > =============
> >
> > diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst
> > index 042c418..15d35ae 100644
> > --- a/Documentation/filesystems/proc.rst
> > +++ b/Documentation/filesystems/proc.rst
> > @@ -961,6 +961,7 @@ You may not have all of these fields.
> > LowFree: 4432 kB
> > SwapTotal: 0 kB
> > SwapFree: 0 kB
> > + SwapAvailable: 0 kB
> > Dirty: 968 kB
> > Writeback: 0 kB
> > AnonPages: 861800 kB
> > @@ -1032,6 +1033,9 @@ SwapTotal
> > SwapFree
> > Memory which has been evicted from RAM, and is temporarily
> > on the disk
> > +SwapAvailable
> > + The memory savings when use swap devices. it takes zram
> > + compression ratio into considerations, when zram is used
>
> Trailing whitespace?
>
> Did you run your patch through scripts/checkpatch.pl first before
> sending it out?
>
OK, I'll be careful next time.
>
> > Dirty
> > Memory which is waiting to get written back to the disk
> > Writeback
> > diff --git a/drivers/block/zram/zcomp.h b/drivers/block/zram/zcomp.h
> > index 40f6420..9c9cb96 100644
> > --- a/drivers/block/zram/zcomp.h
> > +++ b/drivers/block/zram/zcomp.h
> > @@ -40,4 +40,12 @@ int zcomp_decompress(struct zcomp_strm *zstrm,
> > const void *src, unsigned int src_len, void *dst);
> >
> > bool zcomp_set_max_streams(struct zcomp *comp, int num_strm);
> > +#ifdef CONFIG_ZRAM
> > +int get_zram_major(void);
> > +#else
> > +int get_zram_major(void)
> > +{
> > + return -1;
> > +}
> > +#endif
> > #endif /* _ZCOMP_H_ */
> > diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> > index fcaf275..8f527e0 100644
> > --- a/drivers/block/zram/zram_drv.c
> > +++ b/drivers/block/zram/zram_drv.c
> > @@ -59,6 +59,10 @@ static void zram_free_page(struct zram *zram, size_t index);
> > static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec,
> > u32 index, int offset, struct bio *bio);
> >
> > +int get_zram_major(void)
> > +{
> > + return zram_major;
>
> Why does anyone need the zram major number?
>
Swapfile.c will use zram major to determine whether it is a zram device.
I plan to change it to internal interface later.
>
> > +}
> >
> > static int zram_slot_trylock(struct zram *zram, u32 index)
> > {
> > @@ -1040,6 +1044,19 @@ static ssize_t compact_store(struct device *dev,
> > return len;
> > }
> >
> > +static ssize_t min_compr_ratio_show(struct device *dev,
> > + struct device_attribute *attr, char *buf)
> > +{
> > + struct zram *zram = dev_to_zram(dev);
> > + ssize_t ret;
> > +
> > + down_read(&zram->init_lock);
> > + ret = scnprintf(buf, PAGE_SIZE, "%d\n", atomic_read(&zram->stats.min_compr_ratio));
> > + up_read(&zram->init_lock);
>
> You are using an atomic variable _AND_ a read lock? Are you sure that
> makes sense?
>
> And please use sysfs_emit() for sysfs files.
>
It refers to mm_stat_show functioin.
down_read(&zram->init_lock);
....
ret = scnprintf(buf, PAGE_SIZE,
"%8llu %8llu %8llu %8lu %8ld %8llu %8lu %8llu %8llu\n",
...
(u64)atomic64_read(&zram->stats.same_pages),
atomic_long_read(&pool_stats.pages_compacted),
(u64)atomic64_read(&zram->stats.huge_pages),
(u64)atomic64_read(&zram->stats.huge_pages_since));
up_read(&zram->init_lock);
>
> > +
> > + return ret;
> > +}
> > +
> > static ssize_t io_stat_show(struct device *dev,
> > struct device_attribute *attr, char *buf)
> > {
> > @@ -1132,6 +1149,7 @@ static ssize_t debug_stat_show(struct device *dev,
> > return ret;
> > }
> >
> > +static DEVICE_ATTR_RO(min_compr_ratio);
> > static DEVICE_ATTR_RO(io_stat);
> > static DEVICE_ATTR_RO(mm_stat);
> > #ifdef CONFIG_ZRAM_WRITEBACK
> > @@ -1859,6 +1877,7 @@ static struct attribute *zram_disk_attrs[] = {
> > &dev_attr_idle.attr,
> > &dev_attr_max_comp_streams.attr,
> > &dev_attr_comp_algorithm.attr,
> > + &dev_attr_min_compr_ratio.attr,
> > #ifdef CONFIG_ZRAM_WRITEBACK
> > &dev_attr_backing_dev.attr,
> > &dev_attr_writeback.attr,
> > diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h
> > index 80c3b43..5717e06 100644
> > --- a/drivers/block/zram/zram_drv.h
> > +++ b/drivers/block/zram/zram_drv.h
> > @@ -88,6 +88,7 @@ struct zram_stats {
> > atomic64_t bd_reads; /* no. of reads from backing device */
> > atomic64_t bd_writes; /* no. of writes from backing device */
> > #endif
> > + atomic_t min_compr_ratio;
> > };
> >
> > struct zram {
> > diff --git a/fs/proc/meminfo.c b/fs/proc/meminfo.c
> > index 6fa761c..34a174b 100644
> > --- a/fs/proc/meminfo.c
> > +++ b/fs/proc/meminfo.c
> > @@ -86,6 +86,7 @@ static int meminfo_proc_show(struct seq_file *m, void *v)
> >
> > show_val_kb(m, "SwapTotal: ", i.totalswap);
> > show_val_kb(m, "SwapFree: ", i.freeswap);
> > + show_val_kb(m, "SwapAvailable: ", count_avail_swaps());
> > show_val_kb(m, "Dirty: ",
> > global_node_page_state(NR_FILE_DIRTY));
> > show_val_kb(m, "Writeback: ",
> > diff --git a/include/linux/swap.h b/include/linux/swap.h
> > index bb48893..deed141 100644
> > --- a/include/linux/swap.h
> > +++ b/include/linux/swap.h
> > @@ -515,6 +515,8 @@ extern int init_swap_address_space(unsigned int type, unsigned long nr_pages);
> > extern void exit_swap_address_space(unsigned int type);
> > extern struct swap_info_struct *get_swap_device(swp_entry_t entry);
> > sector_t swap_page_sector(struct page *page);
> > +extern void update_zram_zstats(void);
> > +extern u64 count_avail_swaps(void);
> >
> > static inline void put_swap_device(struct swap_info_struct *si)
> > {
> > @@ -689,6 +691,15 @@ static inline swp_entry_t get_swap_page(struct page *page)
> > return entry;
> > }
> >
> > +void update_zram_zstats(void)
> > +{
> > +}
> > +
> > +u64 count_avail_swaps(void)
> > +{
> > + return 0;
> > +}
> > +
> > #endif /* CONFIG_SWAP */
> >
> > #ifdef CONFIG_THP_SWAP
> > diff --git a/mm/swapfile.c b/mm/swapfile.c
> > index 1e07d1c..5ce5100 100644
> > --- a/mm/swapfile.c
> > +++ b/mm/swapfile.c
> > @@ -44,6 +44,7 @@
> > #include <asm/tlbflush.h>
> > #include <linux/swapops.h>
> > #include <linux/swap_cgroup.h>
> > +#include "../drivers/block/zram/zram_drv.h"
>
> That's a big hint that this is not correct, please do not do this :(
>
> The core kernel should not depend on a random block driver's code.
>
> thanks,
>
> greg k-h
Yes, it's a problem.
Using callback function to realize this function is under consideration.
thanks for your reply.
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