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Fri, 22 Mar 2024 17:43:03 -0700 (PDT) MIME-Version: 1.0 References: <01b0b8e8-af1d-4fbe-951e-278e882283fd@linux.dev> In-Reply-To: From: Yosry Ahmed Date: Fri, 22 Mar 2024 17:42:27 -0700 Message-ID: Subject: Re: [External] Re: [bug report] mm/zswap :memory corruption after zswap_load(). To: Barry Song <21cnbao@gmail.com> Cc: Zhongkun He , Chengming Zhou , Johannes Weiner , Andrew Morton , linux-mm , wuyun.abel@bytedance.com, zhouchengming@bytedance.com, Nhat Pham , Kairui Song , Minchan Kim , David Hildenbrand , Chris Li , Ying Content-Type: text/plain; charset="UTF-8" X-Rspamd-Queue-Id: 95B6840013 X-Rspam-User: X-Stat-Signature: 9fzqc6om6rqksj6f44i91zqryoottied X-Rspamd-Server: rspam03 X-HE-Tag: 1711154585-264164 X-HE-Meta: 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 Tt/Blbrx A6EilxHySmbP2cNO3P//3CpECdleVRB75mrfruLlPxqBIhh3WCaaLcbUtoZsEGcMwSKGAg6LzQRnvDlnE4YU0EhTjkxYCjZlrLqNEWZNjHt3p8d1V+nZ03WBerUyQhnGFc7rAT2qM9WIIop/9j/LvBKJC4/L3HuS4W9bKAx1cS1V0zUFNerZYTD2Qb5TbNY83j1N0+9pwZ/tqgMgzjXyrjIWKsSqXpdVs0Y05/l2FBKt2MKtVh97cyRMXLw== 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: [..] > > > This is only a problem when we skip the swapcache during swapin. > > Otherwise the swapcache synchronizes this. I wonder how much does > > skipping the swapcache buy us on recent kernels? This optimization was > > introduced a long time ago. > > Still performs quite good. according to kairui's data: > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=13ddaf26be324a7f951891ecd9ccd04466d27458 > > Before: 10934698 us > After: 11157121 us > Cached: 13155355 us (Dropping SWP_SYNCHRONOUS_IO flag) That's 17.9% slower if we use the swapcache. Commit 0bcac06f27d7 ("mm, swap: skip swapcache for swapin of synchronous device") says: """ This patch aims to reduce swap-in latency by skipping swapcache if the swap device is synchronous device like rw_page based device. It enhances 45% my swapin test(5G sequential swapin, no readahead, from 2.41sec to 1.64sec). """ So went from 45% to 17.9%, we are getting close :) > > BTW, zram+zswap seems pointless from the first beginning. it seems a wrong > configuration for users. if this case is really happening, could we > simply fix it Yeah we can do that. Zhongkun said they have a use case for zram+zswap tho, but I don't know what it is. If we can find a better (yet still simple) fix, then I would prefer that. Otherwise enforcing the use of the swapcache when zswap is enabled sounds like a viable option. > by: > > diff --git a/mm/memory.c b/mm/memory.c > index b7cab8be8632..6742d1428373 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -3999,7 +3999,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) > swapcache = folio; > > if (!folio) { > - if (data_race(si->flags & SWP_SYNCHRONOUS_IO) && > + if (!is_zswap_enabled() && data_race(si->flags & > SWP_SYNCHRONOUS_IO) && > __swap_count(entry) == 1) { > /* > * Prevent parallel swapin from proceeding with