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Sat, 09 Nov 2019 03:01:39 -0800 (PST) To: Jens Axboe , io-uring@vger.kernel.org References: From: Pavel Begunkov Autocrypt: addr=asml.silence@gmail.com; prefer-encrypt=mutual; keydata= mQINBFmKBOQBEAC76ZFxLAKpDw0bKQ8CEiYJRGn8MHTUhURL02/7n1t0HkKQx2K1fCXClbps bdwSHrhOWdW61pmfMbDYbTj6ZvGRvhoLWfGkzujB2wjNcbNTXIoOzJEGISHaPf6E2IQx1ik9 6uqVkK1OMb7qRvKH0i7HYP4WJzYbEWVyLiAxUj611mC9tgd73oqZ2pLYzGTqF2j6a/obaqha +hXuWTvpDQXqcOZJXIW43atprH03G1tQs7VwR21Q1eq6Yvy2ESLdc38EqCszBfQRMmKy+cfp W3U9Mb1w0L680pXrONcnlDBCN7/sghGeMHjGKfNANjPc+0hzz3rApPxpoE7HC1uRiwC4et83 CKnncH1l7zgeBT9Oa3qEiBlaa1ZCBqrA4dY+z5fWJYjMpwI1SNp37RtF8fKXbKQg+JuUjAa9 Y6oXeyEvDHMyJYMcinl6xCqCBAXPHnHmawkMMgjr3BBRzODmMr+CPVvnYe7BFYfoajzqzq+h EyXSl3aBf0IDPTqSUrhbmjj5OEOYgRW5p+mdYtY1cXeK8copmd+fd/eTkghok5li58AojCba jRjp7zVOLOjDlpxxiKhuFmpV4yWNh5JJaTbwCRSd04sCcDNlJj+TehTr+o1QiORzc2t+N5iJ NbILft19Izdn8U39T5oWiynqa1qCLgbuFtnYx1HlUq/HvAm+kwARAQABtDFQYXZlbCBCZWd1 bmtvdiAoc2lsZW5jZSkgPGFzbWwuc2lsZW5jZUBnbWFpbC5jb20+iQJOBBMBCAA4FiEE+6Ju PTjTbx479o3OWt5b1Glr+6UFAlmKBOQCGwMFCwkIBwIGFQgJCgsCBBYCAwECHgECF4AACgkQ Wt5b1Glr+6WxZA//QueaKHzgdnOikJ7NA/Vq8FmhRlwgtP0+E+w93kL+ZGLzS/cUCIjn2f4Q Mcutj2Neg0CcYPX3b2nJiKr5Vn0rjJ/suiaOa1h1KzyNTOmxnsqE5fmxOf6C6x+NKE18I5Jy xzLQoktbdDVA7JfB1itt6iWSNoOTVcvFyvfe5ggy6FSCcP+m1RlR58XxVLH+qlAvxxOeEr/e aQfUzrs7gqdSd9zQGEZo0jtuBiB7k98t9y0oC9Jz0PJdvaj1NZUgtXG9pEtww3LdeXP/TkFl HBSxVflzeoFaj4UAuy8+uve7ya/ECNCc8kk0VYaEjoVrzJcYdKP583iRhOLlZA6HEmn/+Gh9 4orG67HNiJlbFiW3whxGizWsrtFNLsSP1YrEReYk9j1SoUHHzsu+ZtNfKuHIhK0sU07G1OPN 2rDLlzUWR9Jc22INAkhVHOogOcc5ajMGhgWcBJMLCoi219HlX69LIDu3Y34uIg9QPZIC2jwr 24W0kxmK6avJr7+n4o8m6sOJvhlumSp5TSNhRiKvAHB1I2JB8Q1yZCIPzx+w1ALxuoWiCdwV M/azguU42R17IuBzK0S3hPjXpEi2sK/k4pEPnHVUv9Cu09HCNnd6BRfFGjo8M9kZvw360gC1 reeMdqGjwQ68o9x0R7NBRrtUOh48TDLXCANAg97wjPoy37dQE7e5Ag0EWYoE5AEQAMWS+aBV IJtCjwtfCOV98NamFpDEjBMrCAfLm7wZlmXy5I6o7nzzCxEw06P2rhzp1hIqkaab1kHySU7g dkpjmQ7Jjlrf6KdMP87mC/Hx4+zgVCkTQCKkIxNE76Ff3O9uTvkWCspSh9J0qPYyCaVta2D1 Sq5HZ8WFcap71iVO1f2/FEHKJNz/YTSOS/W7dxJdXl2eoj3gYX2UZNfoaVv8OXKaWslZlgqN jSg9wsTv1K73AnQKt4fFhscN9YFxhtgD/SQuOldE5Ws4UlJoaFX/yCoJL3ky2kC0WFngzwRF Yo6u/KON/o28yyP+alYRMBrN0Dm60FuVSIFafSqXoJTIjSZ6olbEoT0u17Rag8BxnxryMrgR dkccq272MaSS0eOC9K2rtvxzddohRFPcy/8bkX+t2iukTDz75KSTKO+chce62Xxdg62dpkZX xK+HeDCZ7gRNZvAbDETr6XI63hPKi891GeZqvqQVYR8e+V2725w+H1iv3THiB1tx4L2bXZDI DtMKQ5D2RvCHNdPNcZeldEoJwKoA60yg6tuUquvsLvfCwtrmVI2rL2djYxRfGNmFMrUDN1Xq F3xozA91q3iZd9OYi9G+M/OA01husBdcIzj1hu0aL+MGg4Gqk6XwjoSxVd4YT41kTU7Kk+/I 5/Nf+i88ULt6HanBYcY/+Daeo/XFABEBAAGJAjYEGAEIACAWIQT7om49ONNvHjv2jc5a3lvU aWv7pQUCWYoE5AIbDAAKCRBa3lvUaWv7pfmcEACKTRQ28b1y5ztKuLdLr79+T+LwZKHjX++P 4wKjEOECCcB6KCv3hP+J2GCXDOPZvdg/ZYZafqP68Yy8AZqkfa4qPYHmIdpODtRzZSL48kM8 LRzV8Rl7J3ItvzdBRxf4T/Zseu5U6ELiQdCUkPGsJcPIJkgPjO2ROG/ZtYa9DvnShNWPlp+R uPwPccEQPWO/NP4fJl2zwC6byjljZhW5kxYswGMLBwb5cDUZAisIukyAa8Xshdan6C2RZcNs rB3L7vsg/R8UCehxOH0C+NypG2GqjVejNZsc7bgV49EOVltS+GmGyY+moIzxsuLmT93rqyII 5rSbbcTLe6KBYcs24XEoo49Zm9oDA3jYvNpeYD8rDcnNbuZh9kTgBwFN41JHOPv0W2FEEWqe JsCwQdcOQ56rtezdCJUYmRAt3BsfjN3Jn3N6rpodi4Dkdli8HylM5iq4ooeb5VkQ7UZxbCWt UVMKkOCdFhutRmYp0mbv2e87IK4erwNHQRkHUkzbsuym8RVpAZbLzLPIYK/J3RTErL6Z99N2 m3J6pjwSJY/zNwuFPs9zGEnRO4g0BUbwGdbuvDzaq6/3OJLKohr5eLXNU3JkT+3HezydWm3W OPhauth7W0db74Qd49HXK0xe/aPrK+Cp+kU1HRactyNtF8jZQbhMCC8vMGukZtWaAwpjWiiH bA== Subject: Re: [PATCH RFC v2] io_uring: limit inflight IO Message-ID: <6945baa5-7539-1d67-fcb5-5642e81994a8@gmail.com> Date: Sat, 9 Nov 2019 14:01:23 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.0 MIME-Version: 1.0 In-Reply-To: Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="w5DUW3Pmp5UzgiKDlBHp6SalI1fwMVRFR" Sender: io-uring-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --w5DUW3Pmp5UzgiKDlBHp6SalI1fwMVRFR Content-Type: multipart/mixed; boundary="LHwWRQ0ZtTOplnfncTWROmMAUx9f7okjA"; protected-headers="v1" From: Pavel Begunkov To: Jens Axboe , io-uring@vger.kernel.org Message-ID: <6945baa5-7539-1d67-fcb5-5642e81994a8@gmail.com> Subject: Re: [PATCH RFC v2] io_uring: limit inflight IO References: In-Reply-To: --LHwWRQ0ZtTOplnfncTWROmMAUx9f7okjA Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 09/11/2019 00:10, Jens Axboe wrote: > Here's a modified version for discussion. Instead of sizing this on the= > specific ring, just size it based on the max allowable CQ ring size. I > think this should be safer, and won't risk breaking existing use cases > out there. >=20 > The reasoning here is that we already limit the ring sizes globally, > they are under ulimit memlock protection. With this on top, we have som= e > sort of safe guard for the system as a whole as well, whereas before we= > had none. Even a small ring size can keep queuing IO. >=20 > Let me know what you guys think... >=20 > diff --git a/fs/io_uring.c b/fs/io_uring.c > index 29ea1106132d..0d8c3b1612af 100644 > --- a/fs/io_uring.c > +++ b/fs/io_uring.c > @@ -737,6 +737,25 @@ static struct io_kiocb *io_get_fallback_req(struct= io_ring_ctx *ctx) > return NULL; > } > =20 > +static bool io_req_over_limit(struct io_ring_ctx *ctx) > +{ > + unsigned inflight; > + > + /* > + * This doesn't need to be super precise, so only check every once > + * in a while. > + */ > + if (ctx->cached_sq_head & ctx->sq_mask) > + return false; > + > + /* > + * Use 2x the max CQ ring size > + */ > + inflight =3D ctx->cached_sq_head - > + (ctx->cached_cq_tail + atomic_read(&ctx->cached_cq_overflow)); > + return inflight >=3D 2 * IORING_MAX_CQ_ENTRIES; > +} ctx->cached_cq_tail protected by ctx->completion_lock and can be changed asynchronously. That's a not synchronised access, so=20 formally (probably) breaks the memory model. False values shouldn't be a problem here, but anyway. > + > static struct io_kiocb *io_get_req(struct io_ring_ctx *ctx, > struct io_submit_state *state) > { > @@ -744,9 +763,11 @@ static struct io_kiocb *io_get_req(struct io_ring_= ctx *ctx, > struct io_kiocb *req; > =20 > if (!percpu_ref_tryget(&ctx->refs)) > - return NULL; > + return ERR_PTR(-ENXIO); > =20 > if (!state) { > + if (unlikely(io_req_over_limit(ctx))) > + goto out_limit; > req =3D kmem_cache_alloc(req_cachep, gfp); > if (unlikely(!req)) > goto fallback; > @@ -754,6 +775,8 @@ static struct io_kiocb *io_get_req(struct io_ring_c= tx *ctx, > size_t sz; > int ret; > =20 > + if (unlikely(io_req_over_limit(ctx))) > + goto out_limit; > sz =3D min_t(size_t, state->ios_left, ARRAY_SIZE(state->reqs)); > ret =3D kmem_cache_alloc_bulk(req_cachep, gfp, sz, state->reqs); > =20 > @@ -789,8 +812,9 @@ static struct io_kiocb *io_get_req(struct io_ring_c= tx *ctx, > req =3D io_get_fallback_req(ctx); > if (req) > goto got_it; > +out_limit: > percpu_ref_put(&ctx->refs); > - return NULL; > + return ERR_PTR(-EBUSY); > } > =20 > static void io_free_req_many(struct io_ring_ctx *ctx, void **reqs, int= *nr) > @@ -3016,9 +3040,9 @@ static int io_submit_sqes(struct io_ring_ctx *ctx= , unsigned int nr, > unsigned int sqe_flags; > =20 > req =3D io_get_req(ctx, statep); > - if (unlikely(!req)) { > + if (unlikely(IS_ERR(req))) { > if (!submitted) > - submitted =3D -EAGAIN; > + submitted =3D PTR_ERR(req); > break; > } > if (!io_get_sqring(ctx, &req->submit)) { > @@ -3039,8 +3063,10 @@ static int io_submit_sqes(struct io_ring_ctx *ct= x, unsigned int nr, > if (link && (sqe_flags & IOSQE_IO_DRAIN)) { > if (!shadow_req) { > shadow_req =3D io_get_req(ctx, NULL); > - if (unlikely(!shadow_req)) > + if (unlikely(IS_ERR(shadow_req))) { > + shadow_req =3D NULL; > goto out; > + } > shadow_req->flags |=3D (REQ_F_IO_DRAIN | REQ_F_SHADOW_DRAIN); > refcount_dec(&shadow_req->refs); > } >=20 --=20 Pavel Begunkov --LHwWRQ0ZtTOplnfncTWROmMAUx9f7okjA-- --w5DUW3Pmp5UzgiKDlBHp6SalI1fwMVRFR Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAEBCAAdFiEE+6JuPTjTbx479o3OWt5b1Glr+6UFAl3GnIMACgkQWt5b1Glr +6VUNBAApE8nu733+L96mHZSV8G++ctHpBIb1WucLECLOb4Agad45E3A87m1oIJC NcP2kv/0gQo0EXUfwAVbQkB3lHn/yFjkUspIbAeXKvQOOy89g83O2Khel5DjD+F6 +8EC0NM68pxkvCoXlSF2UWMauLShzZKmubJEIeXQB29eeFUfjNp52ofMo0058MPW 1LKdpTcmaq9BopmmXxb8WHFZUVJBuiQlR3SHyk/5No4oL2ZMSaYd9FEJ9uYawzje h5KIo/X8zvtCyKVpgWaal8/ReooS0bPqDB0wZ4n0yfjPreACUtp2I8bHtGxr9gdq C8mbVVw5PDDScjWliTpiN8lBp2+t8EVjcY9dVG0UVO5dOGSCELWzmdJQh8kiWiA8 Qm96BoMtEm0U4Flw3aBCfIl1QYD0IK6qqKlXL1n0xShNHm42urT0quMo5WjHCGZf D+NHTzlS2bIPZ1i0aGvJVRGNUmBdEvI2+xbHbs6y64N4Sb0rl34op0XgXwAGG/78 cuqCaI4Y98SOLuCZM1UIxlqoEx7Iwhf7xjQ3xzfLlh73jLc/+UXLSfpPYY7DqSRc 8vPrVL5v2nTLOORX2sAIBr9C5yGI4qwPGbQzd/N8g7Ekrz2zdZfVXXMMdyz01oGO oPU+hedkcU0fFRVIOBRb6oKoEhHipus59SvvpqHAH7vElanLbao= =l6xC -----END PGP SIGNATURE----- --w5DUW3Pmp5UzgiKDlBHp6SalI1fwMVRFR--