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Wed, 26 Feb 2025 20:37:49 -0800 (PST) From: Sergey Senozhatsky To: Andrew Morton Cc: Yosry Ahmed , Hillf Danton , Kairui Song , Sebastian Andrzej Siewior , Minchan Kim , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Sergey Senozhatsky Subject: [PATCH v9 14/19] zsmalloc: introduce new object mapping API Date: Thu, 27 Feb 2025 13:35:32 +0900 Message-ID: <20250227043618.88380-15-senozhatsky@chromium.org> X-Mailer: git-send-email 2.48.1.658.g4767266eb4-goog In-Reply-To: <20250227043618.88380-1-senozhatsky@chromium.org> References: <20250227043618.88380-1-senozhatsky@chromium.org> MIME-Version: 1.0 X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 7F0584000A X-Stat-Signature: 3e4pygcd5ihh65kotogbkf5mj78jgh34 X-Rspam-User: X-HE-Tag: 1740631070-565746 X-HE-Meta: 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 8CvL43xO 9ZsPak+kJ5A7QAMHX0pQxTWviGENI1BS2SHq4v8v16kcpeAxx5TXoJXX/G0artnEDi4yya198b3BJchYbaH0klXkaEbIVqCBcCdw+VSZQn2X/aIVg+J1apG0MsMTxINXEhyf8cmk+GBW8iAYEiEvlz1JOQu58AotL3KAjj61Wd5UVs5fIM5bUWrz9oTnDDEnC9IQiDAf0vEuXVVQdN2t+9hae6P7jKm0eJqMADfCYEC0L/jLVMeSYw+DR4GGoxb4JBKHFtFxobheNnQMETJsrqUKnuRcyEEmDn6Ec3OmwyltjGmFdh0rsGYnKHHAvtEdZy3B0 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: List-Subscribe: List-Unsubscribe: Current object mapping API is a little cumbersome. First, it's inconsistent, sometimes it returns with page-faults disabled and sometimes with page-faults enabled. Second, and most importantly, it enforces atomicity restrictions on its users. zs_map_object() has to return a liner object address which is not always possible because some objects span multiple physical (non-contiguous) pages. For such objects zsmalloc uses a per-CPU buffer to which object's data is copied before a pointer to that per-CPU buffer is returned back to the caller. This leads to another, final, issue - extra memcpy(). Since the caller gets a pointer to per-CPU buffer it can memcpy() data only to that buffer, and during zs_unmap_object() zsmalloc will memcpy() from that per-CPU buffer to physical pages that object in question spans across. New API splits functions by access mode: - zs_obj_read_begin(handle, local_copy) Returns a pointer to handle memory. For objects that span two physical pages a local_copy buffer is used to store object's data before the address is returned to the caller. Otherwise the object's page is kmap_local mapped directly. - zs_obj_read_end(handle, buf) Unmaps the page if it was kmap_local mapped by zs_obj_read_begin(). - zs_obj_write(handle, buf, len) Copies len-bytes from compression buffer to handle memory (takes care of objects that span two pages). This does not need any additional (e.g. per-CPU) buffers and writes the data directly to zsmalloc pool pages. In terms of performance, on a synthetic and completely reproducible test that allocates fixed number of objects of fixed sizes and iterates over those objects, first mapping in RO then in RW mode: OLD API ======= 3 first results out of 10 369,205,778 instructions # 0.80 insn per cycle 40,467,926 branches # 113.732 M/sec 369,002,122 instructions # 0.62 insn per cycle 40,426,145 branches # 189.361 M/sec 369,036,706 instructions # 0.63 insn per cycle 40,430,860 branches # 204.105 M/sec [..] NEW API ======= 3 first results out of 10 265,799,293 instructions # 0.51 insn per cycle 29,834,567 branches # 170.281 M/sec 265,765,970 instructions # 0.55 insn per cycle 29,829,019 branches # 161.602 M/sec 265,764,702 instructions # 0.51 insn per cycle 29,828,015 branches # 189.677 M/sec [..] T-test on all 10 runs ===================== Difference at 95.0% confidence -1.03219e+08 +/- 55308.7 -27.9705% +/- 0.0149878% (Student's t, pooled s = 58864.4) The old API will stay around until the remaining users switch to the new one. After that we'll also remove zsmalloc per-CPU buffer and CPU hotplug handling. The split of map(RO) and map(WO) into read_{begin/end}/write is suggested by Yosry Ahmed. Suggested-by: Yosry Ahmed Signed-off-by: Sergey Senozhatsky --- include/linux/zsmalloc.h | 8 +++ mm/zsmalloc.c | 125 +++++++++++++++++++++++++++++++++++++++ 2 files changed, 133 insertions(+) diff --git a/include/linux/zsmalloc.h b/include/linux/zsmalloc.h index a48cd0ffe57d..7d70983cf398 100644 --- a/include/linux/zsmalloc.h +++ b/include/linux/zsmalloc.h @@ -58,4 +58,12 @@ unsigned long zs_compact(struct zs_pool *pool); unsigned int zs_lookup_class_index(struct zs_pool *pool, unsigned int size); void zs_pool_stats(struct zs_pool *pool, struct zs_pool_stats *stats); + +void *zs_obj_read_begin(struct zs_pool *pool, unsigned long handle, + void *local_copy); +void zs_obj_read_end(struct zs_pool *pool, unsigned long handle, + void *handle_mem); +void zs_obj_write(struct zs_pool *pool, unsigned long handle, + void *handle_mem, size_t mem_len); + #endif diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c index 74a7aaebf7a0..147915ba04f9 100644 --- a/mm/zsmalloc.c +++ b/mm/zsmalloc.c @@ -1364,6 +1364,131 @@ void zs_unmap_object(struct zs_pool *pool, unsigned long handle) } EXPORT_SYMBOL_GPL(zs_unmap_object); +void *zs_obj_read_begin(struct zs_pool *pool, unsigned long handle, + void *local_copy) +{ + struct zspage *zspage; + struct zpdesc *zpdesc; + unsigned long obj, off; + unsigned int obj_idx; + struct size_class *class; + void *addr; + + /* Guarantee we can get zspage from handle safely */ + read_lock(&pool->lock); + obj = handle_to_obj(handle); + obj_to_location(obj, &zpdesc, &obj_idx); + zspage = get_zspage(zpdesc); + + /* Make sure migration doesn't move any pages in this zspage */ + zspage_read_lock(zspage); + read_unlock(&pool->lock); + + class = zspage_class(pool, zspage); + off = offset_in_page(class->size * obj_idx); + + if (off + class->size <= PAGE_SIZE) { + /* this object is contained entirely within a page */ + addr = kmap_local_zpdesc(zpdesc); + addr += off; + } else { + size_t sizes[2]; + + /* this object spans two pages */ + sizes[0] = PAGE_SIZE - off; + sizes[1] = class->size - sizes[0]; + addr = local_copy; + + memcpy_from_page(addr, zpdesc_page(zpdesc), + off, sizes[0]); + zpdesc = get_next_zpdesc(zpdesc); + memcpy_from_page(addr + sizes[0], + zpdesc_page(zpdesc), + 0, sizes[1]); + } + + if (!ZsHugePage(zspage)) + addr += ZS_HANDLE_SIZE; + + return addr; +} +EXPORT_SYMBOL_GPL(zs_obj_read_begin); + +void zs_obj_read_end(struct zs_pool *pool, unsigned long handle, + void *handle_mem) +{ + struct zspage *zspage; + struct zpdesc *zpdesc; + unsigned long obj, off; + unsigned int obj_idx; + struct size_class *class; + + obj = handle_to_obj(handle); + obj_to_location(obj, &zpdesc, &obj_idx); + zspage = get_zspage(zpdesc); + class = zspage_class(pool, zspage); + off = offset_in_page(class->size * obj_idx); + + if (off + class->size <= PAGE_SIZE) { + if (!ZsHugePage(zspage)) + off += ZS_HANDLE_SIZE; + handle_mem -= off; + kunmap_local(handle_mem); + } + + zspage_read_unlock(zspage); +} +EXPORT_SYMBOL_GPL(zs_obj_read_end); + +void zs_obj_write(struct zs_pool *pool, unsigned long handle, + void *handle_mem, size_t mem_len) +{ + struct zspage *zspage; + struct zpdesc *zpdesc; + unsigned long obj, off; + unsigned int obj_idx; + struct size_class *class; + + /* Guarantee we can get zspage from handle safely */ + read_lock(&pool->lock); + obj = handle_to_obj(handle); + obj_to_location(obj, &zpdesc, &obj_idx); + zspage = get_zspage(zpdesc); + + /* Make sure migration doesn't move any pages in this zspage */ + zspage_read_lock(zspage); + read_unlock(&pool->lock); + + class = zspage_class(pool, zspage); + off = offset_in_page(class->size * obj_idx); + + if (off + class->size <= PAGE_SIZE) { + /* this object is contained entirely within a page */ + void *dst = kmap_local_zpdesc(zpdesc); + + if (!ZsHugePage(zspage)) + off += ZS_HANDLE_SIZE; + memcpy(dst + off, handle_mem, mem_len); + kunmap_local(dst); + } else { + /* this object spans two pages */ + size_t sizes[2]; + + off += ZS_HANDLE_SIZE; + sizes[0] = PAGE_SIZE - off; + sizes[1] = mem_len - sizes[0]; + + memcpy_to_page(zpdesc_page(zpdesc), off, + handle_mem, sizes[0]); + zpdesc = get_next_zpdesc(zpdesc); + memcpy_to_page(zpdesc_page(zpdesc), 0, + handle_mem + sizes[0], sizes[1]); + } + + zspage_read_unlock(zspage); +} +EXPORT_SYMBOL_GPL(zs_obj_write); + /** * zs_huge_class_size() - Returns the size (in bytes) of the first huge * zsmalloc &size_class.