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Received: from willy by casper.infradead.org with local (Exim 4.98.1 #2 (Red Hat Linux)) id 1tyrOU-00000004M53-2Dfn; Sun, 30 Mar 2025 12:04:02 +0000 Date: Sun, 30 Mar 2025 13:04:02 +0100 From: Matthew Wilcox To: Luis Chamberlain Cc: brauner@kernel.org, jack@suse.cz, tytso@mit.edu, adilger.kernel@dilger.ca, linux-ext4@vger.kernel.org, riel@surriel.com, hannes@cmpxchg.org, oliver.sang@intel.com, dave@stgolabs.net, david@redhat.com, axboe@kernel.dk, hare@suse.de, david@fromorbit.com, djwong@kernel.org, ritesh.list@gmail.com, linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org, linux-mm@kvack.org, gost.dev@samsung.com, p.raghav@samsung.com, da.gomez@samsung.com Subject: Re: [PATCH 1/3] mm/migrate: add might_sleep() on __migrate_folio() Message-ID: References: <20250330064732.3781046-1-mcgrof@kernel.org> <20250330064732.3781046-2-mcgrof@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250330064732.3781046-2-mcgrof@kernel.org> X-Rspam-User: X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 7EFDD4000B X-Stat-Signature: 5bpm54s5dnnbjkjxs5bpbdi84qnj3cbu X-HE-Tag: 1743336262-255388 X-HE-Meta: U2FsdGVkX18vgn1agadu6KCyQnRUpPmhXMMd3ddH/fLti69X3uwfGUj9FxPknI9O2WLu5byLjovN9rY5ad4rI0qCE4uSoP44RXtRdllY7l6rXHSffO8G4okSdsPrMU9iZ0fa/k4aGSHGCshpcfZHymhTVleZJmX6DRsNFKfj8ZgP0GQmbtNyj2Uy1bG/lX9EQWVyA2R5vyeSm4viRf8dhCiW4S9EGocFMZDg4zsa5E3els/AbdsIfSKgPkW4tzo9Gm/KAgYlI2ExW0m3k7LlG1D9D5i8GXEt9BWnRYa5/aYqxuGA0co0fDTIEw/I5xAogdUgG8Msdnp3G+c5eqWWzR6nMvKG2mm1c33c+0xSbyTpGwDqh684lst6/SkiaMA+005fIF44udY+adybCnojU7dk8nnTqyo7VauhYnFgF1KGQn5fVjemnYHhJO42UONOOxXMqManJNSqP6ATKyg/lefHULIWmIjvNEC5KAh4aiqiaJpB6QX/de3TiTJJv2G/qSLGrY9QwmXOkFzGdDoRBAlkITpCz/v+mksl1kwbutzq0xmGE9D62A7v50wfpgrE8C1l/1n6804BjP+KcP9EJ+IzbRelXaDUlAVg7jCEMw1Uo3lZNVX1GLRMmSpZf2lYnb1GjPSrFaKNR/HCGLnCGtJ2eYbHgUmokqdFlldd6KErHROy/4cyDqQ3lkYuPoVwnd6DbIs7DKTR9ppLpNTgHls2aZITHokeyIW/8tZYjr7gjqDDudNqTG3NxeDMZ9feqaJyWXtSAIge800PzY5te8Kk5F1fRiBGaV4GO69PJNN9WnTjW4az0ytfn9j2/fsReObnV0M02LQqXL0W6+GlnfiaFTMhzIu+c+i/31ZPDH+TwedDw16Fd/3c6SNefFGnfCNnes9gVndBOshADPJwo0H4n4ad3B0ccVf9sOaC9rjqq+l0mKZHHP2+XsD/iZzgXRsMcE4HWqDTiGdafri RVT3LINP +chEK6Id3XgBcjQL589nQuIhkpHaMroT1ExfEhe2Dsd3RDsXjaYSAaTV/bfnF+RaytP1Gd8A8luXgu516NkOp93/K9jChQT1AE6lr6yNNfl+tHBhkt6vXXooJeuhVT75CnaGJbbs4aO/5yhz71OuZ/yTHhX+eSvjalNa+S0xrJg+YLvkdraiXJvUBjrFmnTO5YPqSY041rIFyYVFOYxPVUwzr80l//sTE8f+7W50SHjE3O7vc2OGVhgMBWpfLurQ9csWCnydSNB6yrgh1E36OLDmP5K2Cn4zdSfqLRwHLB6aZ+V0nYmNH2NTl9gMlmHbFgO9sXGIKPk+ppRJ1usohQCKjUIPjEWPHJAao 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 Sat, Mar 29, 2025 at 11:47:30PM -0700, Luis Chamberlain wrote: > However tracing shows that folio_mc_copy() *isn't* being called > as often as we'd expect from buffer_migrate_folio_norefs() path > as we're likely bailing early now thanks to the check added by commit > 060913999d7a ("mm: migrate: support poisoned recover from migrate > folio"). Umm. You're saying that most folios we try to migrate have extra refs? That seems unexpected; does it indicate a bug in 060913999d7a? > +++ b/mm/migrate.c > @@ -751,6 +751,8 @@ static int __migrate_folio(struct address_space *mapping, struct folio *dst, > { > int rc, expected_count = folio_expected_refs(mapping, src); > > + might_sleep(); We deliberately don't sleep when the folio is only a single page. So this needs to be: might_sleep_if(folio_test_large(folio)); > /* Check whether src does not have extra refs before we do more work */ > if (folio_ref_count(src) != expected_count) > return -EAGAIN; > -- > 2.47.2 >