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From: Yosry Ahmed To: Nhat Pham Cc: akpm@linux-foundation.org, hannes@cmpxchg.org, chengming.zhou@linux.dev, linux-mm@kvack.org, kernel-team@meta.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] zswap: do not crash the kernel on decompression failure Message-ID: References: <20250227001445.1099203-1-nphamcs@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Migadu-Flow: FLOW_OUT X-Stat-Signature: cy31f875t99p3oq8gip6qgwwr4fqcqne X-Rspamd-Queue-Id: AD842180006 X-Rspam-User: X-Rspamd-Server: rspam01 X-HE-Tag: 1740795617-920802 X-HE-Meta: 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 lolT7cgo TqQzHi76g6JM5lZt6QeuMX94t8i6DQqFqwGiHQWGDhXj9VZYzVOZmrrFn3gO/2R3jftyNOMsf5AiI/BdqrnKMsFT9+VmUYjU/f9JKp/Ksmfkty4w59wN998G0m9wTAWIsW9kFBlsdtBcWDvZcq1fL3jX3xY8qwTmYnboIlQyKaKkbm/ok+ob+Yqx5KE8qkpXW/woQcw4IF5nVyYb0QmQVd6TRk5o2QpRxlWd5zqxxD/0m2TY= 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 Fri, Feb 28, 2025 at 06:08:16PM -0800, Nhat Pham wrote: > On Thu, Feb 27, 2025 at 1:55 PM Yosry Ahmed wrote: > > > > On Thu, Feb 27, 2025 at 01:46:29PM -0800, Nhat Pham wrote: > > > On Wed, Feb 26, 2025 at 5:19 PM Yosry Ahmed wrote: > > > > > > > > On Wed, Feb 26, 2025 at 04:14:45PM -0800, Nhat Pham wrote: > > > > > Currently, we crash the kernel when a decompression failure occurs in > > > > > zswap (either because of memory corruption, or a bug in the compression > > > > > algorithm). This is overkill. We should only SIGBUS the unfortunate > > > > > process asking for the zswap entry on zswap load, and skip the corrupted > > > > > entry in zswap writeback. The former is accomplished by returning true > > > > > from zswap_load(), indicating that zswap owns the swapped out content, > > > > > but without flagging the folio as up-to-date. The process trying to swap > > > > > in the page will check for the uptodate folio flag and SIGBUS (see > > > > > do_swap_page() in mm/memory.c for more details). > > > > > > > > We should call out the extra xarray walks and their perf impact (if > > > > any). > > > > > > Lemme throw this in a quick and dirty test. I doubt there's any > > > impact, but since I'm reworking this patch for a third version anyway > > > might as well. > > > > It's likely everything is cache hot and the impact is minimal, but let's > > do the due diligence. > > > > Yeah I ran some kernel building tests for 5 times, and found basically > no difference: > > With the new scheme: > > real: mean: 125.1s, stdev: 0.12s > > user: mean: 3265.23s, stdev: 9.62s > > sys: mean: 2156.41s, stdev: 13.98s > > > The old scheme: > > real: mean: 125.78s, stdev: 0.45s > > user: mean: 3287.18s, stdev: 5.95s > > sys: mean: 2177.08s, stdev: 26.52s > > > Honestly, eyeballing the results, the mean difference is probably > smaller than between-run variance. :) Thanks for checking, that's good. Let's include that in the commit message too.