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Mon, 03 Feb 2020 22:23:46 -0800 (PST) Received: from localhost.localdomain ([106.254.212.20]) by smtp.gmail.com with ESMTPSA id u26sm21880240pfn.46.2020.02.03.22.23.39 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 03 Feb 2020 22:23:45 -0800 (PST) From: sj38.park@gmail.com To: akpm@linux-foundation.org Cc: SeongJae Park , acme@kernel.org, alexander.shishkin@linux.intel.com, amit@kernel.org, brendan.d.gregg@gmail.com, brendanhiggins@google.com, cai@lca.pw, colin.king@canonical.com, corbet@lwn.net, dwmw@amazon.com, jolsa@redhat.com, kirill@shutemov.name, mark.rutland@arm.com, mgorman@suse.de, minchan@kernel.org, mingo@redhat.com, namhyung@kernel.org, peterz@infradead.org, rdunlap@infradead.org, rostedt@goodmis.org, sj38.park@gmail.com, vdavydov.dev@gmail.com, linux-mm@kvack.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v3 02/11] mm/damon: Implement region based sampling Date: Tue, 4 Feb 2020 06:23:03 +0000 Message-Id: <20200204062312.19913-3-sj38.park@gmail.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20200204062312.19913-1-sj38.park@gmail.com> References: <20200204062312.19913-1-sj38.park@gmail.com> X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: From: SeongJae Park This commit implements DAMON's basic access check and region based sampling mechanisms. This change would seems make no sense, mainly because it is only a part of the DAMON's logics. Following two commits will make more sense. Basic Access Check ------------------ DAMON basically reports what pages are how frequently accessed. Note that the frequency is not an absolute number of accesses, but a relative frequency among the pages of the target workloads. Users can control the resolution of the reports by setting two time intervals, ``sampling interval`` and ``aggregation interval``. In detail, DAMON checks access to each page per ``sampling interval``, aggregates the results (counts the number of the accesses to each page), and reports the aggregated results per ``aggregation interval``. For the access check of each page, DAMON uses the Accessed bits of PTEs. This is thus similar to common periodic access checks based access tracking mechanisms, which overhead is increasing as the size of the target process grows. Region Based Sampling --------------------- To avoid the unbounded increase of the overhead, DAMON groups a number of adjacent pages that assumed to have same access frequencies into a region. As long as the assumption (pages in a region have same access frequencies) is kept, only one page in the region is required to be checked. Thus, for each ``sampling interval``, DAMON randomly picks one page in each region and clears its Accessed bit. After one more ``sampling interval``, DAMON reads the Accessed bit of the page and increases the access frequency of the region if the bit has set meanwhile. Therefore, the monitoring overhead is controllable by setting the number of regions. Nonetheless, this scheme cannot preserve the quality of the output if the assumption is not kept. Following commit will introduce how we can make the guarantee with best effort. Signed-off-by: SeongJae Park --- mm/damon.c | 642 +++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 642 insertions(+) diff --git a/mm/damon.c b/mm/damon.c index 0687d2b83bb6..5a98c1365ee9 100644 --- a/mm/damon.c +++ b/mm/damon.c @@ -9,9 +9,14 @@ #define pr_fmt(fmt) "damon: " fmt +#include +#include #include #include +#include #include +#include +#include #include #define damon_get_task_struct(t) \ @@ -51,7 +56,30 @@ struct damon_task { struct list_head list; }; +/* + * For each 'sample_interval', DAMON checks whether each region is accessed or + * not. It aggregates and keeps the access information (number of accesses to + * each region) for 'aggr_interval' and then flushes it to the result buffer if + * an 'aggr_interval' surpassed. + * + * All time intervals are in micro-seconds. + */ struct damon_ctx { + unsigned long sample_interval; + unsigned long aggr_interval; + unsigned long min_nr_regions; + + struct timespec64 last_aggregation; + + unsigned char *rbuf; + unsigned int rbuf_len; + unsigned int rbuf_offset; + char *rfile_path; + + struct task_struct *kdamond; + bool kdamond_stop; + spinlock_t kdamond_lock; + struct rnd_state rndseed; struct list_head tasks_list; /* 'damon_task' objects */ @@ -206,6 +234,620 @@ static unsigned int nr_damon_regions(struct damon_task *t) return ret; } +/* + * Get the mm_struct of the given task + * + * Callser should put the mm_struct after use, unless it is NULL. + * + * Returns the mm_struct of the task on success, NULL on failure + */ +static struct mm_struct *damon_get_mm(struct damon_task *t) +{ + struct task_struct *task; + struct mm_struct *mm; + + task = damon_get_task_struct(t); + if (!task) + return NULL; + + mm = get_task_mm(task); + put_task_struct(task); + return mm; +} + +/* + * Size-evenly split a region into 'nr_pieces' small regions + * + * Returns 0 on success, or negative error code otherwise. + */ +static int damon_split_region_evenly(struct damon_ctx *ctx, + struct damon_region *r, unsigned int nr_pieces) +{ + unsigned long sz_orig, sz_piece, orig_end; + struct damon_region *piece = NULL, *next; + unsigned long start; + + if (!r || !nr_pieces) + return -EINVAL; + + orig_end = r->vm_end; + sz_orig = r->vm_end - r->vm_start; + sz_piece = sz_orig / nr_pieces; + + if (!sz_piece) + return -EINVAL; + + r->vm_end = r->vm_start + sz_piece; + next = damon_next_region(r); + for (start = r->vm_end; start + sz_piece <= orig_end; + start += sz_piece) { + piece = damon_new_region(ctx, start, start + sz_piece); + damon_add_region(piece, r, next); + r = piece; + } + if (piece) + piece->vm_end = orig_end; + return 0; +} + +struct region { + unsigned long start; + unsigned long end; +}; + +static unsigned long sz_region(struct region *r) +{ + return r->end - r->start; +} + +static void swap_regions(struct region *r1, struct region *r2) +{ + struct region tmp; + + tmp = *r1; + *r1 = *r2; + *r2 = tmp; +} + +/* + * Find the three regions in an address space + * + * vma the head vma of the target address space + * regions an array of three 'struct region's that results will be saved + * + * This function receives an address space and finds three regions in it which + * separated by the two biggest unmapped regions in the space. Please refer to + * below comments of 'damon_init_regions_of()' function to know why this is + * necessary. + * + * Returns 0 if success, or negative error code otherwise. + */ +static int damon_three_regions_in_vmas(struct vm_area_struct *vma, + struct region regions[3]) +{ + struct region gap = {0,}, first_gap = {0,}, second_gap = {0,}; + struct vm_area_struct *last_vma = NULL; + unsigned long start = 0; + + /* Find two biggest gaps so that first_gap > second_gap > others */ + for (; vma; vma = vma->vm_next) { + if (!last_vma) { + start = vma->vm_start; + last_vma = vma; + continue; + } + gap.start = last_vma->vm_end; + gap.end = vma->vm_start; + if (sz_region(&gap) > sz_region(&second_gap)) { + swap_regions(&gap, &second_gap); + if (sz_region(&second_gap) > sz_region(&first_gap)) + swap_regions(&second_gap, &first_gap); + } + last_vma = vma; + } + + if (!sz_region(&second_gap) || !sz_region(&first_gap)) + return -EINVAL; + + /* Sort the two biggest gaps by address */ + if (first_gap.start > second_gap.start) + swap_regions(&first_gap, &second_gap); + + /* Store the result */ + regions[0].start = start; + regions[0].end = first_gap.start; + regions[1].start = first_gap.end; + regions[1].end = second_gap.start; + regions[2].start = second_gap.end; + regions[2].end = last_vma->vm_end; + + return 0; +} + +/* + * Get the three regions in the given task + * + * Returns 0 on success, negative error code otherwise. + */ +static int damon_three_regions_of(struct damon_task *t, + struct region regions[3]) +{ + struct mm_struct *mm; + int ret; + + mm = damon_get_mm(t); + if (!mm) + return -EINVAL; + + down_read(&mm->mmap_sem); + ret = damon_three_regions_in_vmas(mm->mmap, regions); + up_read(&mm->mmap_sem); + + mmput(mm); + return ret; +} + +/* + * Initialize the monitoring target regions for the given task + * + * t the given target task + * + * Because only a number of small portions of the entire address space + * is acutally mapped to the memory and accessed, monitoring the unmapped + * regions is wasteful. That said, because we can deal with small noises, + * tracking every mapping is not strictly required but could even incur a high + * overhead if the mapping frequently changes or the number of mappings is + * high. Nonetheless, this may seems very weird. DAMON's dynamic regions + * adjustment mechanism, which will be implemented with following commit will + * make this more sense. + * + * For the reason, we convert the complex mappings to three distinct regions + * that cover every mapped areas of the address space. Also the two gaps + * between the three regions are the two biggest unmapped areas in the given + * address space. In detail, this function first identifies the start and the + * end of the mappings and the two biggest unmapped areas of the address space. + * Then, it constructs the three regions as below: + * + * [mappings[0]->start, big_two_unmapped_areas[0]->start) + * [big_two_unmapped_areas[0]->end, big_two_unmapped_areas[1]->start) + * [big_two_unmapped_areas[1]->end, mappings[nr_mappings - 1]->end) + * + * As usual memory map of processes is as below, the gap between the heap and + * the uppermost mmap()-ed region, and the gap between the lowermost mmap()-ed + * region and the stack will be two biggest unmapped regions. Because these + * gaps are exceptionally huge areas in usual address space, excluding these + * two biggest unmapped regions will be sufficient to make a trade-off. + * + * + * + * + * (other mmap()-ed regions and small unmapped regions) + * + * + * + */ +static void damon_init_regions_of(struct damon_ctx *c, struct damon_task *t) +{ + struct damon_region *r; + struct region regions[3]; + int i; + + if (damon_three_regions_of(t, regions)) { + pr_err("Failed to get three regions of task %lu\n", t->pid); + return; + } + + /* Set the initial three regions of the task */ + for (i = 0; i < 3; i++) { + r = damon_new_region(c, regions[i].start, regions[i].end); + damon_add_region_tail(r, t); + } + + /* Split the middle region into 'min_nr_regions - 2' regions */ + r = damon_nth_region_of(t, 1); + if (damon_split_region_evenly(c, r, c->min_nr_regions - 2)) + pr_warn("Init middle region failed to be split\n"); +} + +/* Initialize '->regions_list' of every task */ +static void kdamond_init_regions(struct damon_ctx *ctx) +{ + struct damon_task *t; + + damon_for_each_task(ctx, t) + damon_init_regions_of(ctx, t); +} + +/* + * Check whether the given region has accessed since the last check + * + * mm 'mm_struct' for the given virtual address space + * r the region to be checked + */ +static void kdamond_check_access(struct damon_ctx *ctx, + struct mm_struct *mm, struct damon_region *r) +{ + pte_t *pte = NULL; + pmd_t *pmd = NULL; + spinlock_t *ptl; + + if (follow_pte_pmd(mm, r->sampling_addr, NULL, &pte, &pmd, &ptl)) + goto mkold; + + /* Read the page table access bit of the page */ + if (pte && pte_young(*pte)) + r->nr_accesses++; +#ifdef CONFIG_TRANSPARENT_HUGEPAGE + else if (pmd && pmd_young(*pmd)) + r->nr_accesses++; +#endif /* CONFIG_TRANSPARENT_HUGEPAGE */ + + spin_unlock(ptl); + +mkold: + /* mkold next target */ + r->sampling_addr = damon_rand(ctx, r->vm_start, r->vm_end); + + if (follow_pte_pmd(mm, r->sampling_addr, NULL, &pte, &pmd, &ptl)) + return; + + if (pte) { + if (pte_young(*pte)) { + clear_page_idle(pte_page(*pte)); + set_page_young(pte_page(*pte)); + } + *pte = pte_mkold(*pte); + } +#ifdef CONFIG_TRANSPARENT_HUGEPAGE + else if (pmd) { + if (pmd_young(*pmd)) { + clear_page_idle(pmd_page(*pmd)); + set_page_young(pte_page(*pte)); + } + *pmd = pmd_mkold(*pmd); + } +#endif + + spin_unlock(ptl); +} + +/* + * Check whether a time interval is elapsed + * + * baseline the time to check whether the interval has elapsed since + * interval the time interval (microseconds) + * + * See whether the given time interval has passed since the given baseline + * time. If so, it also updates the baseline to current time for next check. + * + * Returns true if the time interval has passed, or false otherwise. + */ +static bool damon_check_reset_time_interval(struct timespec64 *baseline, + unsigned long interval) +{ + struct timespec64 now; + + ktime_get_coarse_ts64(&now); + if ((timespec64_to_ns(&now) - timespec64_to_ns(baseline)) / 1000 < + interval) + return false; + *baseline = now; + return true; +} + +/* + * Check whether it is time to flush the aggregated information + */ +static bool kdamond_aggregate_interval_passed(struct damon_ctx *ctx) +{ + return damon_check_reset_time_interval(&ctx->last_aggregation, + ctx->aggr_interval); +} + +/* + * Flush the content in the result buffer to the result file + */ +static void damon_flush_rbuffer(struct damon_ctx *ctx) +{ + ssize_t sz; + loff_t pos; + struct file *rfile; + + while (ctx->rbuf_offset) { + pos = 0; + rfile = filp_open(ctx->rfile_path, O_CREAT | O_RDWR | O_APPEND, + 0644); + if (IS_ERR(rfile)) { + pr_err("Cannot open the result file %s\n", + ctx->rfile_path); + return; + } + + sz = kernel_write(rfile, ctx->rbuf, ctx->rbuf_offset, &pos); + filp_close(rfile, NULL); + + ctx->rbuf_offset -= sz; + } +} + +/* + * Write a data into the result buffer + */ +static void damon_write_rbuf(struct damon_ctx *ctx, void *data, ssize_t size) +{ + if (!ctx->rbuf_len || !ctx->rbuf) + return; + if (ctx->rbuf_offset + size > ctx->rbuf_len) + damon_flush_rbuffer(ctx); + + memcpy(&ctx->rbuf[ctx->rbuf_offset], data, size); + ctx->rbuf_offset += size; +} + +/* + * Flush the aggregated monitoring results to the result buffer + * + * Stores current tracking results to the result buffer and reset 'nr_accesses' + * of each regions. The format for the result buffer is as below: + * + *