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Tue, 11 Feb 2025 22:33:06 -0800 (PST) From: Sergey Senozhatsky To: Andrew Morton Cc: Yosry Ahmed , Kairui Song , Minchan Kim , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Sergey Senozhatsky Subject: [PATCH v5 13/18] zsmalloc: introduce new object mapping API Date: Wed, 12 Feb 2025 15:27:11 +0900 Message-ID: <20250212063153.179231-14-senozhatsky@chromium.org> X-Mailer: git-send-email 2.48.1.502.g6dc24dfdaf-goog In-Reply-To: <20250212063153.179231-1-senozhatsky@chromium.org> References: <20250212063153.179231-1-senozhatsky@chromium.org> MIME-Version: 1.0 X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 449E5C0003 X-Stat-Signature: kn14ij1mxa7f7ndqts6mef6mso9e3kga X-HE-Tag: 1739341988-290931 X-HE-Meta: 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 MH46W5Ia ZkvsjdQvpAm/oUIQ6+bsTfsQ5Vju/1bayXrsc4MRyr4oh4cpG/22i6AONqMs6TQK5bt5hf3cD5td4+fYky6QVPKnLEoiE1k6U71p7DHt6rpoirZyXN1IEirZ4Kmt5ANZiB53cZkufIyzXyGfeuZN0jgytfEeSAAzPKy6Q2wjynDQUAzk7cEzvS+9OBlyWQ+MD4npQiQHisjLJ0jnAtzzJgXbOyMf73LCuL/pvAv8boUAbCWqZhoVgMtYjXwh/x6yBAhoEpaRriaqhgLfMYYhjJdd0VXcUxn/w+dZLSO2qduZ5/3/zblOABezyvw== 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 ======= 10 runs 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 ======= 10 runs 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 [..] 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. Signed-off-by: Sergey Senozhatsky Reviewed-by: Yosry Ahmed --- include/linux/zsmalloc.h | 8 +++ mm/zsmalloc.c | 129 +++++++++++++++++++++++++++++++++++++++ 2 files changed, 137 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 80261bb78cf8..e40268f3b655 100644 --- a/mm/zsmalloc.c +++ b/mm/zsmalloc.c @@ -1401,6 +1401,135 @@ 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; + + WARN_ON(in_interrupt()); + + /* Guarantee we can get zspage from handle safely */ + pool_read_lock(pool); + 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); + pool_read_unlock(pool); + + 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; + + WARN_ON(in_interrupt()); + + /* Guarantee we can get zspage from handle safely */ + pool_read_lock(pool); + 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); + pool_read_unlock(pool); + + 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.