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[188.193.207.173]) by smtp.gmail.com with ESMTPSA id hp12-20020a1709073e0c00b006e02924bf20sm1319405ejc.117.2022.04.01.12.58.11 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 01 Apr 2022 12:58:11 -0700 (PDT) Message-ID: <5226b4ae-33fe-2bee-b88a-240994231d1c@gmail.com> Date: Fri, 1 Apr 2022 21:58:11 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.7.0 Subject: Re: [PATCH v2 3/3] scsi: target: tcmu: Use address_space->invalidate_lock Content-Language: en-US To: Xiaoguang Wang , linux-scsi@vger.kernel.org, target-devel@vger.kernel.org Cc: linux-block@vger.kernel.org References: <20220323134940.31463-1-xiaoguang.wang@linux.alibaba.com> <20220323134940.31463-4-xiaoguang.wang@linux.alibaba.com> From: Bodo Stroesser In-Reply-To: <20220323134940.31463-4-xiaoguang.wang@linux.alibaba.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-scsi@vger.kernel.org On 23.03.22 14:49, Xiaoguang Wang wrote: > Currently tcmu_vma_fault() uses udev->cmdr_lock to avoid concurrent > find_free_blocks(), which unmaps idle pages and truncates them. This > work is really like many filesystem's truncate operations, but they > use address_space->invalidate_lock to protect race. > > This patch replaces cmdr_lock with address_space->invalidate_lock in > tcmu fault procedure, which will also make page-fault have concurrency. > Page fault happens only once for each allocated data page. After the page fault was processed, the page is re-used for many cmds without further page faults. Of course, if find_free_blocks released a page and tcmu after that allocates a new one, another page fault will occur. But that is a very rare case. So, what is the advantage of concurrency here? OTOH, I don't like the switch from tcmu's cmdr_lock to filemap_invalidate_* without a real technical reason. > Signed-off-by: Xiaoguang Wang > --- > drivers/target/target_core_user.c | 14 ++++++++++---- > 1 file changed, 10 insertions(+), 4 deletions(-) > > diff --git a/drivers/target/target_core_user.c b/drivers/target/target_core_user.c > index 9196188504ec..81bfa553cc67 100644 > --- a/drivers/target/target_core_user.c > +++ b/drivers/target/target_core_user.c > @@ -1820,13 +1820,14 @@ static int tcmu_find_mem_index(struct vm_area_struct *vma) > > static struct page *tcmu_try_get_data_page(struct tcmu_dev *udev, uint32_t dpi) > { > + struct address_space *mapping = udev->inode->i_mapping; > struct page *page; > > - mutex_lock(&udev->cmdr_lock); > + filemap_invalidate_lock_shared(mapping); > page = xa_load(&udev->data_pages, dpi); > if (likely(page)) { > get_page(page); > - mutex_unlock(&udev->cmdr_lock); > + filemap_invalidate_unlock_shared(mapping); > return page; > } > > @@ -1836,7 +1837,7 @@ static struct page *tcmu_try_get_data_page(struct tcmu_dev *udev, uint32_t dpi) > */ > pr_err("Invalid addr to data page mapping (dpi %u) on device %s\n", > dpi, udev->name); > - mutex_unlock(&udev->cmdr_lock); > + filemap_invalidate_unlock_shared(mapping); > > return NULL; > } > @@ -3116,6 +3117,7 @@ static void find_free_blocks(void) > loff_t off; > u32 pages_freed, total_pages_freed = 0; > u32 start, end, block, total_blocks_freed = 0; > + struct address_space *mapping; > > if (atomic_read(&global_page_count) <= tcmu_global_max_pages) > return; > @@ -3139,6 +3141,8 @@ static void find_free_blocks(void) > continue; > } > > + mapping = udev->inode->i_mapping; > + filemap_invalidate_lock(mapping); > end = udev->dbi_max + 1; > block = find_last_bit(udev->data_bitmap, end); > if (block == udev->dbi_max) { > @@ -3146,6 +3150,7 @@ static void find_free_blocks(void) > * The last bit is dbi_max, so it is not possible > * reclaim any blocks. > */ > + filemap_invalidate_unlock(mapping); > mutex_unlock(&udev->cmdr_lock); > continue; > } else if (block == end) { > @@ -3159,10 +3164,11 @@ static void find_free_blocks(void) > > /* Here will truncate the data area from off */ > off = udev->data_off + (loff_t)start * udev->data_blk_size; > - unmap_mapping_range(udev->inode->i_mapping, off, 0, 1); > + unmap_mapping_range(mapping, off, 0, 1); > > /* Release the block pages */ > pages_freed = tcmu_blocks_release(udev, start, end - 1); > + filemap_invalidate_unlock(mapping); > mutex_unlock(&udev->cmdr_lock); > > total_pages_freed += pages_freed;