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[124.209.188.1]) by smtp.gmail.com with ESMTPSA id s41-20020a056a0017a900b005871b73e27dsm7674381pfg.33.2023.01.31.17.41.50 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 31 Jan 2023 17:41:53 -0800 (PST) Date: Wed, 1 Feb 2023 10:41:48 +0900 From: Sergey Senozhatsky To: Nhat Pham Cc: akpm@linux-foundation.org, hannes@cmpxchg.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, minchan@kernel.org, ngupta@vflare.org, senozhatsky@chromium.org, sjenning@redhat.com, ddstreet@ieee.org, vitaly.wool@konsulko.com, kernel-team@meta.com Subject: Re: [PATCH] zsmalloc: fix a race with deferred_handles storing Message-ID: References: <20230110231701.326724-1-nphamcs@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230110231701.326724-1-nphamcs@gmail.com> X-Rspamd-Queue-Id: 5EF26A0004 X-Rspamd-Server: rspam09 X-Rspam-User: X-Stat-Signature: fmm8ss8qxwg5on1neyfsf8xnowhg61q3 X-HE-Tag: 1675215715-268083 X-HE-Meta: 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 s4K18Uys UZuYAYUBNJ/KRkOTGlizpYtet0ASEuWIIZaFdIpwdM+otUiZzyjVY6pjCyADqKA+TtmDc2cwvz2mz9GHzulKtaDJzRVYv76CyaTObFunmH4MQIJbRwROmQZed/z3s0gWQBqWZ7ofGth4OL7QTLVl5yaH00gkd6aG5ZnFcW13GfEMNHIjpv4rBU00juO7UGIIK57ac2v0YyKrgkLBmyXe5yKhpeePD7v7d5ZWkU8wret1TQW/PB+N4tuWxB7Gl6S4yrCDs87ESriZesSRPtT/YqIjqprmash7WDhc3+Yi+G+MVFPvv0zb6aOX8cMSqbCidM79HqFvEh30USfMHOOTzGAEIhyiKYMVUUWlGtrEe4cjMKea0lI8CkJRXDqopM+WQTEG5ktAQs2vv0EymMBKVk0AjYg== 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: On (23/01/10 15:17), Nhat Pham wrote: [..] > #ifdef CONFIG_ZPOOL > +static void restore_freelist(struct zs_pool *pool, struct size_class *class, > + struct zspage *zspage) > +{ > + unsigned int obj_idx = 0; > + unsigned long handle, off = 0; /* off is within-page offset */ > + struct page *page = get_first_page(zspage); > + struct link_free *prev_free = NULL; > + void *prev_page_vaddr = NULL; > + > + /* in case no free object found */ > + set_freeobj(zspage, (unsigned int)(-1UL)); I'm not following this. I see how -1UL works for link_free, but this cast of -1UL to 4 bytes looks suspicious. > + while (page) { > + void *vaddr = kmap_atomic(page); > + struct page *next_page; > + > + while (off < PAGE_SIZE) { > + void *obj_addr = vaddr + off; > + > + /* skip allocated object */ > + if (obj_allocated(page, obj_addr, &handle)) { > + obj_idx++; > + off += class->size; > + continue; > + } > + > + /* free deferred handle from reclaim attempt */ > + if (obj_stores_deferred_handle(page, obj_addr, &handle)) > + cache_free_handle(pool, handle); > + > + if (prev_free) > + prev_free->next = obj_idx << OBJ_TAG_BITS; > + else /* first free object found */ > + set_freeobj(zspage, obj_idx); > + > + prev_free = (struct link_free *)vaddr + off / sizeof(*prev_free); > + /* if last free object in a previous page, need to unmap */ > + if (prev_page_vaddr) { > + kunmap_atomic(prev_page_vaddr); > + prev_page_vaddr = NULL; > + } > + > + obj_idx++; > + off += class->size; > + } > + > + /* > + * Handle the last (full or partial) object on this page. > + */ > + next_page = get_next_page(page); > + if (next_page) { > + if (!prev_free || prev_page_vaddr) { > + /* > + * There is no free object in this page, so we can safely > + * unmap it. > + */ > + kunmap_atomic(vaddr); > + } else { > + /* update prev_page_vaddr since prev_free is on this page */ > + prev_page_vaddr = vaddr; > + } A polite and gentle nit: I'd appreciate it if we honored kernel coding styles in zsmalloc a little bit more. Comments, function declarations, etc. I'm personally very happy with https://github.com/vivien/vim-linux-coding-style