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From: Yosry Ahmed To: Sergey Senozhatsky Cc: Andrew Morton , Minchan Kim , Johannes Weiner , Nhat Pham , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH 5/6] zsmalloc: introduce handle mapping API Message-ID: References: <20250127080254.1302026-1-senozhatsky@chromium.org> <20250127080254.1302026-6-senozhatsky@chromium.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250127080254.1302026-6-senozhatsky@chromium.org> X-Migadu-Flow: FLOW_OUT X-Rspamd-Queue-Id: 7EFA614000A X-Stat-Signature: fnjc3sdjwphy5muhc8cj5nizbst7haog X-Rspamd-Server: rspam08 X-Rspam-User: X-HE-Tag: 1738013196-363277 X-HE-Meta: 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 PCqltI3d PJUMCbGHVSbf17EMh6+4DcUliPnCcD0xSgIrXp4Z9Y50A4kwZyhbI9E0tlmiWVoAUfkAVkOV179onTHiu/b8ST9Q1/1b+ayg6NxRWQ2N6QEo1fLdysCS6S3Dkd+gh8szzsZjYZT3rgMaWsDl0zvOg2SdbxQNkocPtQMo2JwHdRIvuzZ2qmWrgHYzziiG6C0MqzMj31adDeKuCGHMK2gjCNPsPig== 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: On Mon, Jan 27, 2025 at 04:59:30PM +0900, Sergey Senozhatsky wrote: > Introduce new API to map/unmap zsmalloc handle/object. The key > difference is that this API does not impose atomicity restrictions > on its users, unlike zs_map_object() which returns with page-faults > and preemption disabled I think that's not entirely accurate, see below. [..] > @@ -1309,12 +1297,14 @@ void *zs_map_object(struct zs_pool *pool, unsigned long handle, > goto out; > } > > - /* this object spans two pages */ > - zpdescs[0] = zpdesc; > - zpdescs[1] = get_next_zpdesc(zpdesc); > - BUG_ON(!zpdescs[1]); > + ret = area->vm_buf; > + /* disable page faults to match kmap_local_page() return conditions */ > + pagefault_disable(); Is this accurate/necessary? I am looking at kmap_local_page() and I don't see it. Maybe that's remnant from the old code using kmap_atomic()? > + if (mm != ZS_MM_WO) { > + /* this object spans two pages */ > + zs_obj_copyin(area->vm_buf, zpdesc, off, class->size); > + } > > - ret = __zs_map_object(area, zpdescs, off, class->size); > out: > if (likely(!ZsHugePage(zspage))) > ret += ZS_HANDLE_SIZE;