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b=k9bCE3ZlPTDEwakexIITAXv0tMPzY+7+iotOPgcNMyjKKBedUUwISrlUjsBF6fFH4 zoQ7ehW6kyvlTfiIyWJbgGiFRCsZeFXR066U2N0Cc4AJjDKBG6BZqRrbkIb2iAv392 N2RvQ5+R2lbP6sM93JS2Do+hFO/F/Of3LXkg0h3IskXSSaG5WoF0heGBDHmSzJ/oTd A0xe54DghmTTzehjRQKex2moLZ+Ad/arvLfvk5Gu2EmRARn+tWFuLqajbfOlUmJkB5 kIauQBRoCm1Riqzem0rXWW/SJ5+zDqyr75ySzzQRX+Px1b/PbXcS4WMIU8gQbYdH/V 9Uo5tiw8xeWgg== From: SeongJae Park To: Nhat Pham Cc: SeongJae Park , Andrew Morton , Chengming Zhou , Johannes Weiner , Takero Funaki , Yosry Ahmed , kernel-team@meta.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [RFC PATCH] mm/zswap: store compression failed page as-is Date: Thu, 31 Jul 2025 09:43:56 -0700 Message-Id: <20250731164356.15198-1-sj@kernel.org> X-Mailer: git-send-email 2.39.5 In-Reply-To: References: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Stat-Signature: umb3czbkr5qenocewo3oqfgj88jadxo8 X-Rspam-User: X-Rspamd-Queue-Id: 63C3640002 X-Rspamd-Server: rspam02 X-HE-Tag: 1753980240-940792 X-HE-Meta: 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 4hIgmyt9 nlRPdluA9YLiazyAhVgWz5AdTp6uv1PexiETaJqFqXqzwyUEkk91ahmexn5OBk0nl4ougKT/bWYlRFPiE31pcxTwTU+6itTuNeosZC1+2WQRuPTz3wYPG4htPuB5m16MdUHjjMxwUJt4yDnOU2WSl6VBxHRZdVZW5EUsxUDHLQuNzpTi0AlBEcPwJPdZdVeUIuKcYtqoqfM7dZxcN8a5UG6qyJJAodo5XiCzRW98DTedM2nNo6GkawOTBwMGu/TgauJwGCfik13oZOs9eWcIBqpuNGPT6n5viiwAls6sE0lLPMQeY9hhP7/p/mtL0YtlWVVuI8n/dVGQL9zLowtUjTHlBfw== 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 Wed, 30 Jul 2025 17:22:51 -0700 Nhat Pham wrote: > On Wed, Jul 30, 2025 at 5:21 PM Nhat Pham wrote: > > > > On Wed, Jul 30, 2025 at 4:41 PM SeongJae Park wrote: > > > > This might not be safe. > > > > It's conceivable that in zswap_compress(), some compression algorithm > > "successfully" compresses a page to the same size (comp_ret == 0). We > > hand that to zsmalloc, which happily stores the page. > > > > When we "decompress" the page again, we will attempt to > > memcpy_to_folio from a bogus address (the handle from zsmalloc). > > > > So, in zswap_compress, you have to treat both comp_ret == 0 and dlen > > == PAGE_SIZE as "compression failure". > > Meant to say comp_ret != 0 here... sorry for the confusion... No worry, thank you for clarifying! Thanks, SJ