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(unknown []) by gzga-smtp-mtada-g0-3 (Coremail) with SMTP id _____wD3_7Q6Hx1qsb0MAw--.47504S6; Mon, 01 Jun 2026 13:57:22 +0800 (CST) From: Chi Zhiling To: linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: "Matthew Wilcox (Oracle)" , Jan Kara , Andrew Morton , Hugh Dickins , Baolin Wang , Chi Zhiling Subject: [PATCH v2 4/5] mm/shmem: remove page-copy fallback in shmem read path Date: Mon, 1 Jun 2026 13:57:03 +0800 Message-ID: <20260601055704.167436-5-chizhiling@163.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260601055704.167436-1-chizhiling@163.com> References: <20260601055704.167436-1-chizhiling@163.com> Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-CM-TRANSID:_____wD3_7Q6Hx1qsb0MAw--.47504S6 X-Coremail-Antispam: 1Uf129KBjvJXoWxAF1DWF1xCFW7Kr17Wr17ZFb_yoWrCw4xpF W3KasIyrWxJw43Gr17JFs8Za4rK3s3JFWUJFyfG3WfA3Z3tryrKFyUta4F9FWfJ34UC3WI gw4qyr1UWa1UAr7anT9S1TB71UUUUU7qnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDUYxBIdaVFxhVjvjDU0xZFpf9x07jeE_NUUUUU= X-CM-SenderInfo: hfkl6xxlol0wi6rwjhhfrp/xtbC+AK5V2odH0JEmQAA3j From: Chi Zhiling This is perp patch for folio batch support which removing the fallback to page-copy mode from shmem reads. The existing hwpoison fallback would require fetching the same folio multiple times to read its each pages, which complicates the batching model. Instead, move hwpoison handling into copy_each_pages_to_iter(), allowing the error path to be centralized. This simplifies the shmem fast read path and avoids special-case handling that conflicts with folio batching support. Signed-off-by: Chi Zhiling --- mm/shmem.c | 63 +++++++++++++++++++++++++++++------------------------- 1 file changed, 34 insertions(+), 29 deletions(-) diff --git a/mm/shmem.c b/mm/shmem.c index b08118fbd275..cac355685e49 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -3353,6 +3353,30 @@ static size_t copy_zero_to_iter(size_t bytes, struct iov_iter *i) return written; } +static size_t copy_pages_to_iter(struct folio *folio, size_t offset, + size_t bytes, struct iov_iter *i, int *error) +{ + struct page *page; + unsigned long off, nr, ret, written = 0; + + do { + page = folio_page(folio, offset >> PAGE_SHIFT); + if (PageHWPoison(page)) { + *error = -EIO; + break; + } + + off = offset_in_page(offset); + nr = min(PAGE_SIZE - off, bytes - written); + + ret = copy_page_to_iter(page, off, nr, i); + offset += ret; + written += ret; + } while (written < bytes && ret == nr); + + return written; +} + static ssize_t shmem_file_read_iter(struct kiocb *iocb, struct iov_iter *to) { struct file *file = iocb->ki_filp; @@ -3365,10 +3389,8 @@ static ssize_t shmem_file_read_iter(struct kiocb *iocb, struct iov_iter *to) for (;;) { struct folio *folio = NULL; - struct page *page = NULL; unsigned long nr, ret; loff_t end_offset, i_size = i_size_read(inode); - bool fallback_page_copy = false; size_t fsize; if (unlikely(iocb->ki_pos >= i_size)) @@ -3376,25 +3398,13 @@ static ssize_t shmem_file_read_iter(struct kiocb *iocb, struct iov_iter *to) index = iocb->ki_pos >> PAGE_SHIFT; error = shmem_get_folio(inode, index, 0, &folio, SGP_READ); + if (folio) + folio_unlock(folio); if (error) { if (error == -EINVAL) error = 0; break; } - if (folio) { - folio_unlock(folio); - - page = folio_file_page(folio, index); - if (PageHWPoison(page)) { - folio_put(folio); - error = -EIO; - break; - } - - if (folio_test_large(folio) && - folio_test_has_hwpoisoned(folio)) - fallback_page_copy = true; - } /* * We must evaluate after, since reads (unlike writes) @@ -3406,12 +3416,9 @@ static ssize_t shmem_file_read_iter(struct kiocb *iocb, struct iov_iter *to) folio_put(folio); break; } - end_offset = min_t(loff_t, i_size, iocb->ki_pos + to->count); - if (folio && likely(!fallback_page_copy)) - fsize = folio_size(folio); - else - fsize = PAGE_SIZE; + fsize = folio ? folio_size(folio) : PAGE_SIZE; offset = iocb->ki_pos & (fsize - 1); + end_offset = min_t(loff_t, i_size, iocb->ki_pos + to->count); nr = min_t(loff_t, end_offset - iocb->ki_pos, fsize - offset); if (folio) { @@ -3420,12 +3427,8 @@ static ssize_t shmem_file_read_iter(struct kiocb *iocb, struct iov_iter *to) * virtual addresses, take care about potential aliasing * before reading the page on the kernel side. */ - if (mapping_writably_mapped(mapping)) { - if (likely(!fallback_page_copy)) - flush_dcache_folio(folio); - else - flush_dcache_page(page); - } + if (mapping_writably_mapped(mapping)) + flush_dcache_folio(folio); /* * Mark the folio accessed if we read the beginning. @@ -3436,10 +3439,10 @@ static ssize_t shmem_file_read_iter(struct kiocb *iocb, struct iov_iter *to) * Ok, we have the page, and it's up-to-date, so * now we can copy it to user space... */ - if (likely(!fallback_page_copy)) + if (likely(!folio_contain_hwpoisoned_page(folio))) ret = copy_folio_to_iter(folio, offset, nr, to); else - ret = copy_page_to_iter(page, offset, nr, to); + ret = copy_pages_to_iter(folio, offset, nr, to, &error); folio_put(folio); } else if (user_backed_iter(to)) { /* @@ -3462,6 +3465,8 @@ static ssize_t shmem_file_read_iter(struct kiocb *iocb, struct iov_iter *to) if (!iov_iter_count(to)) break; + if (unlikely(error)) + break; if (ret < nr) { error = -EFAULT; break; -- 2.43.0