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Howlett" , ryan.roberts@arm.com, Vlastimil Babka , lance.yang@linux.dev, linux-kernel@vger.kernel.org, nphamcs@gmail.com, shikemeng@huaweicloud.com, kernel-team@meta.com, Alexandre Ghiti Subject: Re: [PATCH v5 04/11] mm: zswap: add range lookup for large-folio swapin Message-ID: References: <20260722152043.2273289-1-usama.arif@linux.dev> <20260722152043.2273289-5-usama.arif@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260722152043.2273289-5-usama.arif@linux.dev> X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 9DA541C0007 X-Stat-Signature: wrg3u43j9hgg8r3b8eeu5u7z9anxwr67 X-HE-Tag: 1784764864-61772 X-HE-Meta: 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 jPMvbHPr kztkR5LRYw4iFg7RjrqwsgGMiNmBMxEQ1ucotjAyczMsjgi/VrhQWk9gT/q6y7VegpTn83exOA+tzx8B0CAX7KtIa9qUzoKQs3VxOlw5K+LU1eiVgeVwvynGkHUC9sqFkKOQZgK4KKgnWwlnATLpNni/LG08wwTDnp+CYiGxLSIUCutDXGNHkKen6//TCGfHoL+usXbn8ofLqSMCQjWfuQxo5tl08HOB1elw2GQrGvjV5dM6bwteu+xqtxzC02vp8h8Vw9tlqMfnVwMs34gMU9MrbFyqXYONP+yDFS2w+W6thQDRDzeLXUhIHSw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Jul 22, 2026 at 08:19:35AM -0700, Usama Arif wrote: > From: Alexandre Ghiti > > A large folio reaches zswap_load() only when the caller expects > the whole range to be on disk. Zswap still stores large folios as > independent order-0 entries, so reconstructing a large folio from > zswap entries would risk returning partially initialized data. > > Teach zswap_load() to scan the covered range. If no slot is in zswap, > return -ENOENT so swap_read_folio() reads the backing device. If any > slot is still in zswap, fail the large-folio read so the caller can > fall back to per-page swapin. > > Return -EIO rather than -EINVAL for that conflict. Large-folio loads > are now valid requests; the error means zswap cannot safely satisfy > the request from partial per-page compressed state, not that the > request is unsupported. Existing callers only distinguish -ENOENT, > so this is a semantic clarification rather than a behavioral change. > > Add zswap_is_present() so PMD swap-entry consumers can make the same > range decision before attempting PMD-order swapin. > > Signed-off-by: Alexandre Ghiti > Signed-off-by: Usama Arif > --- > include/linux/zswap.h | 6 ++++++ > mm/zswap.c | 42 ++++++++++++++++++++++++++++++++---------- > 2 files changed, 38 insertions(+), 10 deletions(-) > > diff --git a/include/linux/zswap.h b/include/linux/zswap.h > index 30c193a1207e..cd9efcf9dec9 100644 > --- a/include/linux/zswap.h > +++ b/include/linux/zswap.h > @@ -35,6 +35,7 @@ void zswap_lruvec_state_init(struct lruvec *lruvec); > void zswap_folio_swapin(struct folio *folio); > bool zswap_is_enabled(void); > bool zswap_never_enabled(void); > +bool zswap_is_present(swp_entry_t entry, unsigned int nr); > #else > > struct zswap_lruvec_state {}; > @@ -69,6 +70,11 @@ static inline bool zswap_never_enabled(void) > return true; > } > > +static inline bool zswap_is_present(swp_entry_t entry, unsigned int nr) > +{ > + return false; > +} > + > #endif > > #endif /* _LINUX_ZSWAP_H */ > diff --git a/mm/zswap.c b/mm/zswap.c > index 4e76a4a87cdc..384492f1f696 100644 > --- a/mm/zswap.c > +++ b/mm/zswap.c > @@ -1561,6 +1561,23 @@ bool zswap_store(struct folio *folio) > return ret; > } > > +/** > + * zswap_is_present() - is any slot in [entry, entry + nr) in zswap? > + * @entry: base swap entry of the range > + * @nr: number of contiguous slots to check (pass 1 for a single-slot query) > + */ > +bool zswap_is_present(swp_entry_t entry, unsigned int nr) > +{ > + pgoff_t offset = swp_offset(entry); > + struct xarray *tree = swap_zswap_tree(entry); > + unsigned long index = offset; > + > + if (!nr || zswap_never_enabled()) > + return false; > + > + return xa_find(tree, &index, offset + nr - 1, XA_PRESENT); > +} > + > /** > * zswap_load() - load a folio from zswap > * @folio: folio to load > @@ -1573,10 +1590,9 @@ bool zswap_store(struct folio *folio) > * NOT marked up-to-date, so that an IO error is emitted (e.g. do_swap_page() > * will SIGBUS). > * > - * -EINVAL: if the swapped out content was in zswap, but the page belongs > - * to a large folio, which is not supported by zswap. The folio is unlocked, > - * but NOT marked up-to-date, so that an IO error is emitted (e.g. > - * do_swap_page() will SIGBUS). > + * -EIO: if a slot in a large-folio range is unexpectedly still in zswap. > + * The folio is unlocked, but NOT marked up-to-date, so that an IO > + * error is emitted (e.g. do_swap_page() will SIGBUS). > * > * -ENOENT: if the swapped out content was not in zswap. The folio remains > * locked on return. > @@ -1595,13 +1611,19 @@ int zswap_load(struct folio *folio) > return -ENOENT; > > /* > - * Large folios should not be swapped in while zswap is being used, as > - * they are not properly handled. Zswap does not properly load large > - * folios, and a large folio may only be partially in zswap. > + * A large folio reaches zswap_load() only when its whole range is > + * expected to be on disk: PMD swap-entry consumers split before > + * calling into PMD-order swapin whenever any slot is still in zswap. > + * Confirm the range is entirely absent from zswap and return -ENOENT > + * so the caller reads it from disk; if a slot is unexpectedly still in > + * zswap, fail the read rather than return partially-initialized data. > */ > - if (WARN_ON_ONCE(folio_test_large(folio))) { > - folio_unlock(folio); > - return -EINVAL; > + if (folio_test_large(folio)) { > + if (zswap_is_present(swp, folio_nr_pages(folio))) { Is dropping the warning here intentional (for the folio_test_large() && zswap_is_present() case)? > + folio_unlock(folio); > + return -EIO; > + } > + return -ENOENT; > } > > entry = xa_load(tree, offset); > -- > 2.53.0-Meta >