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Tue, 19 Aug 2025 18:13:25 -0700 (PDT) MIME-Version: 1.0 References: <20250819193404.46680-1-sj@kernel.org> In-Reply-To: <20250819193404.46680-1-sj@kernel.org> From: Barry Song <21cnbao@gmail.com> Date: Wed, 20 Aug 2025 13:13:13 +1200 X-Gm-Features: Ac12FXwrLRpJ2ga3pwvuv6cGSCA-Czm3wS4TCkbPm2Umb0bGpsO20qp0BKxK9T0 Message-ID: Subject: Re: [PATCH v4] mm/zswap: store , Herbert Xu Cc: Andrew Morton , Chengming Zhou , Johannes Weiner , Nhat Pham , Yosry Ahmed , kernel-team@meta.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Takero Funaki , David Hildenbrand , Baoquan He , Chris Li , Kairui Song Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: A317C140015 X-Stat-Signature: h4ujxj9dd7axcm67w81pgmrb1of1g1qs X-Rspam-User: X-HE-Tag: 1755652406-315262 X-HE-Meta: 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 tOKsiJMy pKLs4Q4DX4FzE7jf4mrcVdRUjbYuBF6BPfPy2MzkM9mIWwGlYsbKze0hAOaHKeQh3AXXl961+u9pelOfaKyoy/vJ+FdblNbcFHTSK/cN+aa86yLs9i6ba3RNoFHAT3CiD9hKf6zfCheAKJLWDVHaEP+uVgL6D44nUUAZUaBAxlvWOH0HZkZz3xUO3xGlhfxO1t4cdRcsmtu9JVMNDZPSOnqG5iESkkNkYxsK570g9KVIAzzp0BC/q12K+Gjm3LqSlOgXGPny+WnaQowM+gW7ZuS5AKQ3kgHZ7sxfjlSUxGOukwvsGP8Pi2bhvzOAQUko8gNJ81ns9lsXocmNfskqgUR/SsOyvdxUiWVRXqczR21ZixAbb6hUygdW5wc1mON5Fghz9+3Xsl4nokUs76Bi1ZGRN6yln+kChe3kyypFEItGE92G6O19OerIV4dmdlxWv0l/nw/7Yn6+sMJU= 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: [...] > + > + /* > + * If a page cannot be compressed into a size smaller than PAGE_S= IZE, > + * save the content as is without a compression, to keep the LRU = order > + * of writebacks. If writeback is disabled, reject the page sinc= e it > + * only adds metadata overhead. swap_writeout() will put the pag= e back > + * to the active LRU list in the case. > + */ > + if (comp_ret || !dlen) { > + zswap_crypto_compress_fail++; > + dlen =3D PAGE_SIZE; > + } I=E2=80=99m not entirely sure about this. As long as we pass 2*PAGE_SIZE as dst_buf, any error returned by crypto drivers should indicate a bug in the driver that needs to be fixed. There have also been attempts to unify crypto drivers so they consistently return -ENOSPC when the destination buffer would overflow. If that has been achieved, we might be able to reduce the buffer from 2*PAGE_SIZE to just PAGE_SIZE in zswap. There was a long discussion on this here: https://lore.kernel.org/linux-mm/Z7dnPh4tPxLO1UEo@google.com/ I=E2=80=99m not sure of the current status =E2=80=94 do all crypto drivers = now return a consistent -ENOSPC when the compressed size exceeds PAGE_SIZE? From what I recall during that discussion, most drivers already behaved this way, but Sergey Senozhatsky pointed out one or two exceptions. Let=E2=80=99s sync with Herbert: have we reached the stage where all driver= s reliably return -ENOSPC when dst_buf is PAGE_SIZE but the compressed size would exceed it? Thanks Barry