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AJvYcCWj69kACS1vQ83bAKHALHXmuP1TbhMoXxMiHM5Ib6mUXfbqizJ3DuQF46E5V+l1aKMCvTxiW4ABAjQmViLT33FipA8= X-Gm-Message-State: AOJu0Yz+dAOzi4EcoZbDawR1fPOG0Jr0/+TPBUGky/W4/kJQ6Q3lnnWP TsJbkbJojfKVYsig4K/0pPc1FRUAJ/22Qo62RshvkORY/JMJeapVkXOUOMiIOSp8zwHIgkfLKCh Yu4lZ3aGMdkat3nQTz7cL+Q3+S5g= X-Google-Smtp-Source: AGHT+IE3VsycMfHZ9bzfKVao8hyhW0gX2lzQBQdmfcBmuS8LEK6MztSZPYqyzbvuWf2Rr4wNUUS3flPs/0XCFZT1kv4= X-Received: by 2002:a25:8205:0:b0:de6:197b:ff89 with SMTP id 3f1490d57ef6-dfaf65f0993mr8935828276.64.1718064176831; Mon, 10 Jun 2024 17:02:56 -0700 (PDT) MIME-Version: 1.0 References: <20240608023654.3513385-1-yosryahmed@google.com> In-Reply-To: From: Barry Song <21cnbao@gmail.com> Date: Tue, 11 Jun 2024 12:02:45 +1200 Message-ID: Subject: Re: [PATCH v2] mm: zswap: handle incorrect attempts to load of large folios To: Yosry Ahmed Cc: Andrew Morton , Johannes Weiner , Nhat Pham , Chengming Zhou , Baolin Wang , Chris Li , Ryan Roberts , David Hildenbrand , Matthew Wilcox , linux-mm@kvack.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam03 X-Stat-Signature: t5d91icy1wgoeqk8dj84ybeykhnmc58m X-Rspamd-Queue-Id: 0231D180007 X-Rspam-User: X-HE-Tag: 1718064177-988716 X-HE-Meta: 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 Ws0/4+bP ZXU3PGE+bF8Pd7O8v6Q8Et9clMVJsGcQ0FVIBMrG9TpBd0EkPMojzjD9R0mC5zEuZXUgumsjhB9u8D3VtwxokFVpLVpVmwhmZp/TP1xN/BK7pm745d1AAn3Fh6nNgBSUinU3yYiBZki/HhbH8mQy2+iEJcIgvZ9lvJ4m5b2v0K6JMparVq8RCFgpyx2AsAVqbcPHS/U57F9DS59un2VtZ+muPLy5Gm9SP1cSjuZhtfhUEzXnrrWiSO8utLqNXXpofS5Mfda7nFPaZKUYDqA6Ieo1QB4J+B5aXSDd/ 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 Tue, Jun 11, 2024 at 11:41=E2=80=AFAM Yosry Ahmed wrote: > > [..] > > > > > We can't always WARN_ON for large folios, as this will fire even = if > > > > > zswap was never enabled. The alternative is tracking whether zswa= p was > > > > > ever enabled, and checking that instead of checking if any part o= f the > > > > > folio is in zswap. > > > > > > > > > > Basically replacing xa_find(..) with zswap_was_enabled(..) or som= ething. > > > > > > > > My point is that mm core should always fallback > > > > > > > > if (zswap_was_or_is_enabled()) > > > > goto fallback; > > > > > > > > till zswap fixes the issue. This is the only way to enable large fo= lios swap-in > > > > development before we fix zswap. > > > > > > I agree with this, I just want an extra fallback in zswap itself in > > > case something was missed during large folio swapin development (whic= h > > > can evidently happen). > > > > yes. then i feel we only need to warn_on the case mm-core fails to fall= back. > > > > I mean, only WARN_ON is_zswap_ever_enabled&&large folio. there is no > > need to do more. Before zswap brings up the large folio support, mm-cor= e > > will need is_zswap_ever_enabled() to do fallback. > > I don't have a problem with doing it this way instead of checking if > any part of the folio is in zswap. Such a check may be needed for core > MM to fallback to order-0 anyway, as we discussed. But I'd rather have > this as a static key since it will never be changed. right. This is better. > > Also, I still prefer we do not mark the folio as uptodate in this > case. It is one extra line of code to propagate the kernel warning to > userspace as well and make it much more noticeable. right. I have no objection to returning true and skipping mark uptodate. Just searching xa is not so useful as anyway, we have to either fallback in mm-core or bring up large folios in zswap. > > > > > > diff --git a/include/linux/zswap.h b/include/linux/zswap.h > > index 2a85b941db97..035e51ed89c4 100644 > > --- a/include/linux/zswap.h > > +++ b/include/linux/zswap.h > > @@ -36,6 +36,7 @@ void zswap_memcg_offline_cleanup(struct mem_cgroup *m= emcg); > > void zswap_lruvec_state_init(struct lruvec *lruvec); > > void zswap_folio_swapin(struct folio *folio); > > bool is_zswap_enabled(void); > > +bool is_zswap_ever_enabled(void); > > #else > > > > struct zswap_lruvec_state {}; > > @@ -65,6 +66,10 @@ static inline bool is_zswap_enabled(void) > > return false; > > } > > > > +static inline bool is_zswap_ever_enabled(void) > > +{ > > + return false; > > +} > > #endif > > > > #endif /* _LINUX_ZSWAP_H */ > > diff --git a/mm/zswap.c b/mm/zswap.c > > index b9b35ef86d9b..bf2da5d37e47 100644 > > --- a/mm/zswap.c > > +++ b/mm/zswap.c > > @@ -86,6 +86,9 @@ static int zswap_setup(void); > > static bool zswap_enabled =3D IS_ENABLED(CONFIG_ZSWAP_DEFAULT_ON); > > static int zswap_enabled_param_set(const char *, > > const struct kernel_param *); > > + > > +static bool zswap_ever_enable; > > + > > static const struct kernel_param_ops zswap_enabled_param_ops =3D { > > .set =3D zswap_enabled_param_set, > > .get =3D param_get_bool, > > @@ -136,6 +139,11 @@ bool is_zswap_enabled(void) > > return zswap_enabled; > > } > > > > +bool is_zswap_ever_enabled(void) > > +{ > > + return zswap_enabled || zswap_ever_enabled; > > +} > > + > > /********************************* > > * data structures > > **********************************/ > > @@ -1734,6 +1742,7 @@ static int zswap_setup(void) > > pr_info("loaded using pool %s/%s\n", pool->tfm_name, > > zpool_get_type(pool->zpools[0])); > > list_add(&pool->list, &zswap_pools); > > + zswap_ever_enabled =3D true; > > zswap_has_pool =3D true; > > } else { > > pr_err("pool creation failed\n"); > > Thanks Barry