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Miller" , Johannes Weiner , Nhat Pham , Chengming Zhou , Nick Terrell , David Sterba , SJ Park , Chris Li , Giovanni Cabiddu , Suman Kumar Chakraborty , linux-crypto@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 8E73E40009 X-Stat-Signature: m3cextojhechumzr5wwrsqfh4gfaiii6 X-Spam-Status: No, score=-21.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS, USER_AGENT_GIT,USER_IN_DEF_DKIM_WL autolearn=ham autolearn_force=no version=4.0.1 X-Rspam-User: X-HE-Tag: 1792694007-464720 X-HE-Meta: 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 kiFJjURT LdlB4qDiJWrpAyqaTmkyNh2OlVrQLwIUwdi5LPdGYrgjt96P/vqngU5LcLzsS4YQJaNf6ndeLO4MtdnHJ8GG6G3+H5mAm8jGhTjl1jxhtaItsuIv+4Sdf+743wNkpV4E9Jxiwa/i/izcDGBpiQiSqp2fmLLDxD9RQ7yv2jOHKKUjkTD6Fv8mhsDtZ2VqILSWGTTYvA28APU4Clo6NrF9TP/q4FzybGHz4AaWAlZM8YZ7BUEThFx0Bavy2zrXXH3V/i3AfTwDNdupVfQJWximdxIVB/PX9Qi2ILRwr+YDYaUeOHv/NG9Ms5a7ZX/7k/3t2AlkdVx84D4ZoMbiIR0YO5vs8rWNax1k6jxMFX9H35KL1lFFlXlsRMihdBtqm/5yE4k/tcfv6yQO5QkDPKkPIQJc0LYtfXTLmGw8kfBLXmjJ8XN1uMzB8YN2ydYpN1NCtJnVOo1mDECgaG6mZW1bUaVcCKHbiJwifOqnUDxG2W8A5A6/TWinQ2Y2j2g/6AUfcAwO93B0GvGgWSq1Y460Coz/09XYZXnr+TgKqAa+cwWVspeV9sZ98CSsdF9bv2WzV36SMxjzYL96XuRfbjvFCrfCBy2V03l3KmyXiLLDmNgUcv+vpzSmNgZxV6g== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Thu, Oct 22, 2026 at 09:01:02AM -0700, Yosry Ahmed wrote: > On Thu, Oct 22, 2026 at 8:51 AM Suseendran Bhaskaran > wrote: [...] > > With that unchanged, existing zswap_compress() already accounts -ENOSPC > > vs other error codes when writeback is disabled, except for the > > !comp_ret && dlen >= PAGE_SIZE case mentioned above: > > Is this actually possible? When we changed the buffer size to > PAGE_SIZE, I thought we made sure all compressors wouldn't write > beyond the buffer size. dlen > PAGE_SIZE means buffer overflow, which > is a bigger problem than debugfs stats. Or maybe compressors can set > dlen > PAGE_SIZE but won't actually write to the buffer? I didn't > check. dlen > PAGE_SIZE isn't possible, since all compressors bound their output by the input req->dlen (PAGE_SIZE) as you mentioned, and only set req->dlen <= PAGE_SIZE. The 'dlen >= PAGE_SIZE' check in commit dca4437a5861 ("mm/zswap: store As for the (!comp_ret && dlen == PAGE_SIZE) case specifically, yeah we > should probably use -ENOSPC to count it as poor compression. Ack. > The compt_ret and dlen checks are not super intuitive tbh, I wonder > how they should relate. What is the expected value of dlen if comp_ret > is an error? Is it always 0, or can the compressor set it as a > non-zero value if compression fails? On error (comp_ret != 0), dlen is not guaranteed to be 0. The value left in dlen depends on the compressor used. For example: - zstd, 842, and qat set dlen = 0 on error. - lz4, lz4hc, lzo, lzo-rle (via scomp_acomp_comp_decomp()), deflate, and iaa return the error code without modifying dlen, so dlen remains at its input value (PAGE_SIZE). - hisi_zip sets dlen to the hardware-reported produced bytes even on error. So dlen is only meaningful when !comp_ret. The !dlen check was added in commit dca4437a5861 ("mm/zswap: store > > > - comp_ret = comp_ret ? comp_ret : -EINVAL; > > + comp_ret = comp_ret ? comp_ret : > > + (dlen >= PAGE_SIZE ? -ENOSPC : -EINVAL); > > > > Would you prefer that I narrow Patch 2 to just that change in v2, or drop > > Patch 2 and only send Patch 1? > > Let's figure out what needs to be done for patch 2 first, if anything. Since dlen is only valid when !comp_ret, we could normalize comp_ret first when !comp_ret and then just check 'if (comp_ret)': diff --git a/mm/zswap.c b/mm/zswap.c --- a/mm/zswap.c +++ b/mm/zswap.c @@ -874,19 +874,24 @@ static bool zswap_compress(struct page *page, struct zswap_entry *entry, */ comp_ret = crypto_wait_req(crypto_acomp_compress(acomp_ctx->req), &acomp_ctx->wait); dlen = acomp_ctx->req->dlen; + if (!comp_ret) { + if (dlen == PAGE_SIZE) + comp_ret = -ENOSPC; + else if (WARN_ON_ONCE(!dlen || dlen > PAGE_SIZE)) + comp_ret = -EINVAL; + } /* * If a page cannot be compressed into a size smaller than PAGE_SIZE, * save the content as is without a compression, to keep the LRU order * of writebacks. If writeback is disabled, reject the page since it * only adds metadata overhead. swap_writeout() will put the page back * to the active LRU list in the case. */ - if (comp_ret || !dlen || dlen >= PAGE_SIZE) { + if (comp_ret) { rcu_read_lock(); if (!mem_cgroup_zswap_writeback_enabled( folio_memcg(page_folio(page)))) { rcu_read_unlock(); - comp_ret = comp_ret ? comp_ret : -EINVAL; goto unlock; } Does this look good to you?