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Howlett , ryan.roberts@arm.com, Vlastimil Babka , lance.yang@linux.dev, linux-kernel@vger.kernel.org, nphamcs@gmail.com, shikemeng@huaweicloud.com, yosry@kernel.org, qi.zheng@linux.dev, luizcap@redhat.com, kernel-team@meta.com, Usama Arif Subject: [PATCH v9 16/32] mm: zswap: reject high-order swap cache allocations backed by zswap Date: Thu, 5 Nov 2026 10:39:00 -0800 Message-ID: <20261105183940.2236717-17-usama.arif@linux.dev> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261105183940.2236717-1-usama.arif@linux.dev> References: <20261105183940.2236717-1-usama.arif@linux.dev> X-Archived-By: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Spam-Status: No, score=-18.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=4.0.1 X-Rspamd-Server: rspam09 X-Stat-Signature: axaxwg15s7dh7gsekc8q55u9kbityzzz X-Rspamd-Queue-Id: C593C140009 X-Rspam-User: X-HE-Tag: 1793904092-849463 X-HE-Meta: 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 h5Yx/xOx YVY1DruzxJ0jrnhFRPfYzGdvrBuReRGfId93DzsJmJbKEsnTNdUwJejmzzRQSVMQnq1t42ibm0pZ+W/VmoOffoPqSTFDB55AOfjRieRtQXGHzMBgXFF7AxchjIJgKXwaio7qvJQCZxpKyIyBIGZ49tfAPBwjjLNm6ThXttbtbVoO7ULQTY7/LRhBPpJjRvnL0yAPGjHfWCw09gvubbea3/VvQBguIlWXAqaHn Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 zswap stores swapped-out pages one at a time, so a range of swap slots can be split between zswap entries and the backing device. A high-order swap-cache folio over such a range cannot be read back in one go: the disk read would return stale or zero data for every slot zswap owns. Reject that in __swap_cache_alloc(). Do the check after the folio is in the swap cache: from that point zswap can neither start storing nor start writing back any slot in the range, so the answer is stable. Callers already fall back to order-0, which zswap_load() handles per page. Co-developed-by: Alexandre Ghiti Signed-off-by: Alexandre Ghiti Signed-off-by: Usama Arif --- mm/swap_state.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/mm/swap_state.c b/mm/swap_state.c index a8a486b0403ab..f41e740a91b87 100644 --- a/mm/swap_state.c +++ b/mm/swap_state.c @@ -12,6 +12,7 @@ #include #include #include +#include #include #include #include @@ -482,6 +483,17 @@ static struct folio *__swap_cache_alloc(struct swap_cluster_info *ci, __swap_cache_do_add_folio(ci, folio, entry); spin_unlock(&ci->lock); + /* + * Now that the folio is in the swap cache, zswap can no longer start + * storing or writing back any slot in the range, so this is a stable + * answer. Reject a high-order allocation over a range that already + * has per-page zswap entries. + */ + if (order && zswap_is_present(entry, nr_pages)) { + err = -EBUSY; + goto delete_folio; + } + if (mem_cgroup_swapin_charge_folio(folio, memcg_id, vmf ? vmf->vma->vm_mm : NULL, gfp)) { err = -ENOMEM; -- 2.53.0-Meta