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[91.12.107.109]) by smtp.gmail.com with ESMTPSA id z12sm5549022wrv.68.2021.06.02.00.44.37 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 02 Jun 2021 00:44:37 -0700 (PDT) To: yong w Cc: minchan@kernel.org, ngupta@vflare.org, senozhatsky@chromium.org, axboe@kernel.dk, akpm@linux-foundation.org, songmuchun@bytedance.com, linux-kernel@vger.kernel.org, linux-block@vger.kernel.org, linux-mm@kvack.org References: <13c28e69-cfd9-bcf6-ab77-445c6fa4cc6e@redhat.com> From: David Hildenbrand Organization: Red Hat Subject: Re: [RFC PATCH V1] zram:calculate available memory when zram is used Message-ID: <4350ee16-15d0-1d37-6074-cea5185aac51@redhat.com> Date: Wed, 2 Jun 2021 09:44:36 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.10.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On 02.06.21 02:06, yong w wrote: > Thanks for your reply! > > Indeed, when zram is not triggered, MemAvalible will be greater than Memtotal. > As you said, this modification will have program compatibility issues, > when there > are some user space scripts use MemAvailable for calculation. > > How about providing another proc interface? > Such as /proc/xxx, When execute “cat /proc/xxx”, it returns "available > + swapfree - swapfree * compress ratio" value. Good question. What would be an appropriate name and description for this entry? We do have in /proc/meminfo already: MemTotal: MemAvailable: SwapTotal: SwapFree: I wonder if we could add an entry either for "swapfree - swapfree * compress" or "swapfree * compress". But even then, I struggle to find a fitting name. We could either define something like "SwapAvailable:" An estimate of how much swap space is available for starting new applications. Note that SwapAvailable is different to SwapFree when swap compression, as implemented by zram, is being performed. So a user can compute "TotalAvailable = MemAvailable + SwapAvailable". or if that doesn't make any sense: "TotalAvailable:" An estimate of how much memory and swap space is available for starting new applications. Usually, the value corresponds to "MemAvailable + SwapFree", however, swap compression, as implemented by zram, might allow for making more efficient use of free swap space. I'd prefer the first -- if it makes any sense. You should CC linux-api on follow up patches. > Thanks in advance！ > > > David Hildenbrand 于2021年5月31日周一 下午4:17写道： >> >> On 30.05.21 19:18, yong w wrote: >>> When zram is used, available+Swap free memory is obviously bigger than >>> I actually can use, because zram can compress memory by compression >>> algorithm and zram compressed data will occupy memory too. >>> >>> So, I count the compression rate of zram in the kernel. The available >>> memory is calculated as follows: >>> available + swapfree - swapfree * compress ratio >>> MemAvailable in /proc/meminfo returns available + zram will save space >>> >> >> This will mean that we can easily have MemAvailable > MemTotal, right? >> I'm not sure if there are some user space scripts that will be a little >> disrupted by that. Like calculating "MemUnavailable = MemTotal - >> MemAvailable". >> >> MemAvailable: "An estimate of how much memory is available for starting >> new applications, without swapping" >> >> Although zram isn't "traditional swapping", there is still a performance >> impact when having to go to zram because it adds an indirection and >> requires (de)compression. Similar to having very fast swap space (like >> PMEM). Let's not call something "memory" that doesn't have the same >> semantics as real memory as in "MemTotal". >> >> This doesn't feel right. >> >>> Signed-off-by: wangyong > >>> --- >>> drivers/block/zram/zcomp.h | 1 + >>> drivers/block/zram/zram_drv.c | 4 ++ >>> drivers/block/zram/zram_drv.h | 1 + >>> fs/proc/meminfo.c | 2 +- >>> include/linux/swap.h | 10 +++++ >>> mm/swapfile.c | 95 >>> +++++++++++++++++++++++++++++++++++++++++++ >>> mm/vmscan.c | 1 + >>> 7 files changed, 113 insertions(+), 1 deletion(-) >>> >>> diff --git a/drivers/block/zram/zcomp.h b/drivers/block/zram/zcomp.h >>> index 40f6420..deb2dbf 100644 >>> --- a/drivers/block/zram/zcomp.h >>> +++ b/drivers/block/zram/zcomp.h >>> @@ -40,4 +40,5 @@ 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); >>> +int get_zram_major(void); >>> #endif /* _ZCOMP_H_ */ >>> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c >>> index cf8deec..1c6cbd4 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; >>> +} >>> >>> static int zram_slot_trylock(struct zram *zram, u32 index) >>> { >>> diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h >>> index 6e73dc3..5d8701a 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..f7bf350 100644 >>> --- a/fs/proc/meminfo.c >>> +++ b/fs/proc/meminfo.c >>> @@ -57,7 +57,7 @@ static int meminfo_proc_show(struct seq_file *m, void *v) >>> >>> show_val_kb(m, "MemTotal: ", i.totalram); >>> show_val_kb(m, "MemFree: ", i.freeram); >>> - show_val_kb(m, "MemAvailable: ", available); >>> + show_val_kb(m, "MemAvailable: ", available + count_avail_swaps()); >>> show_val_kb(m, "Buffers: ", i.bufferram); >>> show_val_kb(m, "Cached: ", cached); >>> show_val_kb(m, "SwapCached: ", total_swapcache_pages()); >>> diff --git a/include/linux/swap.h b/include/linux/swap.h >>> index 032485e..3225a2f 100644 >>> --- a/include/linux/swap.h >>> +++ b/include/linux/swap.h >>> @@ -514,6 +514,8 @@ 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) >>> { >>> @@ -684,6 +686,14 @@ static inline swp_entry_t get_swap_page(struct page >>> *page) >>> return entry; >>> } >>> >>> +void update_zram_zstats(void) >>> +{ >>> +} >>> + >>> +u64 count_avail_swaps(void) >>> +{ >>> +} >>> + >>> #endif /* CONFIG_SWAP */ >>> >>> #ifdef CONFIG_THP_SWAP >>> diff --git a/mm/swapfile.c b/mm/swapfile.c >>> index cbb4c07..93a9dcb 100644 >>> --- a/mm/swapfile.c >>> +++ b/mm/swapfile.c >>> @@ -44,6 +44,7 @@ >>> #include >>> #include >>> #include >>> +#include "../drivers/block/zram/zram_drv.h" >>> >>> static bool swap_count_continued(struct swap_info_struct *, pgoff_t, >>> unsigned char); >>> @@ -3408,6 +3409,100 @@ SYSCALL_DEFINE2(swapon, const char __user *, >>> specialfile, int, swap_flags) >>> return error; >>> } >>> >>> +u64 count_avail_swap(struct swap_info_struct *si) >>> +{ >>> + u64 result; >>> + struct zram *z; >>> + unsigned int free; >>> + unsigned int ratio; >>> + >>> + result = 0; >>> + if (!si) >>> + return 0; >>> + >>> + //zram calculate available mem >>> + if (si->flags & SWP_USED && si->swap_map) { >>> + if (si->bdev->bd_disk->major == get_zram_major()) { >>> + z = (struct zram *)si->bdev->bd_disk->private_data; >>> + down_read(&z->init_lock); >>> + ratio = atomic_read(&z->stats.min_compr_ratio); >>> + free = (si->pages << (PAGE_SHIFT - 10)) >>> + - (si->inuse_pages << (PAGE_SHIFT - 10)); >>> + if (!ratio) >>> + result += free / 2; >>> + else >>> + result = free * (100 - 10000 / ratio) / 100; >>> + up_read(&z->init_lock); >>> + } >>> + } else >>> + result += (si->pages << (PAGE_SHIFT - 10)) >>> + - (si->inuse_pages << (PAGE_SHIFT - 10)); >>> + >>> + return result; >>> +} >>> + >>> +u64 count_avail_swaps(void) >>> +{ >>> + int type; >>> + u64 result; >>> + struct swap_info_struct *si; >>> + >>> + result = 0; >>> + spin_lock(&swap_lock); >>> + for (type = 0; type < nr_swapfiles; type++) { >>> + si = swap_info[type]; >>> + spin_lock(&si->lock); >>> + result += count_avail_swap(si); >>> + spin_unlock(&si->lock); >>> + } >>> + spin_unlock(&swap_lock); >>> + >>> + return result; >>> +} >>> + >>> +void update_zram_zstat(struct swap_info_struct *si) >>> +{ >>> + struct zram *z; >>> + struct zram_stats *stat; >>> + int ratio; >>> + u64 orig_size, compr_data_size; >>> + >>> + if (!si) >>> + return; >>> + >>> + //update zram min compress ratio >>> + if (si->flags & SWP_USED && si->swap_map) { >>> + if (si->bdev->bd_disk->major == get_zram_major()) { >>> + z = (struct zram *)si->bdev->bd_disk->private_data; >>> + down_read(&z->init_lock); >>> + stat = &z->stats; >>> + ratio = atomic_read(&stat->min_compr_ratio); >>> + orig_size = atomic64_read(&stat->pages_stored) << PAGE_SHIFT; >>> + compr_data_size = atomic64_read(&stat->compr_data_size); >>> + if (compr_data_size && (!ratio >>> + || ((orig_size * 100) / compr_data_size < ratio))) >>> + atomic_set(&stat->min_compr_ratio, >>> + (orig_size * 100) / compr_data_size); >>> + up_read(&z->init_lock); >>> + } >>> + } >>> +} >>> + >>> +void update_zram_zstats(void) >>> +{ >>> + int type; >>> + struct swap_info_struct *si; >>> + >>> + spin_lock(&swap_lock); >>> + for (type = 0; type < nr_swapfiles; type++) { >>> + si = swap_info[type]; >>> + spin_lock(&si->lock); >>> + update_zram_zstat(si); >>> + spin_unlock(&si->lock); >>> + } >>> + spin_unlock(&swap_lock); >>> +} >>> + >>> void si_swapinfo(struct sysinfo *val) >>> { >>> unsigned int type; >>> diff --git a/mm/vmscan.c b/mm/vmscan.c >>> index eb31452..ffaf59b 100644 >>> --- a/mm/vmscan.c >>> +++ b/mm/vmscan.c >>> @@ -4159,6 +4159,7 @@ static int kswapd(void *p) >>> alloc_order); >>> reclaim_order = balance_pgdat(pgdat, alloc_order, >>> highest_zoneidx); >>> + update_zram_zstats(); >>> if (reclaim_order < alloc_order) >>> goto kswapd_try_sleep; >>> } >>> -- >>> 2.7.4 >> >> >> -- >> Thanks, >> >> David / dhildenb >> > -- Thanks, David / dhildenb