From: Vlastimil Babka <vbabka@suse.cz> To: Alexander Viro <viro@zeniv.linux.org.uk>, Andrew Morton <akpm@linux-foundation.org> Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Michal Hocko <mhocko@kernel.org>, netdev@vger.kernel.org, Eric Dumazet <eric.dumazet@gmail.com>, Vlastimil Babka <vbabka@suse.cz> Subject: [PATCH v2] fs/select: add vmalloc fallback for select(2) Date: Thu, 22 Sep 2016 18:43:59 +0200 [thread overview] Message-ID: <20160922164359.9035-1-vbabka@suse.cz> (raw) The select(2) syscall performs a kmalloc(size, GFP_KERNEL) where size grows with the number of fds passed. We had a customer report page allocation failures of order-4 for this allocation. This is a costly order, so it might easily fail, as the VM expects such allocation to have a lower-order fallback. Such trivial fallback is vmalloc(), as the memory doesn't have to be physically contiguous. Also the allocation is temporary for the duration of the syscall, so it's unlikely to stress vmalloc too much. Note that the poll(2) syscall seems to use a linked list of order-0 pages, so it doesn't need this kind of fallback. [eric.dumazet@gmail.com: fix failure path logic] Signed-off-by: Vlastimil Babka <vbabka@suse.cz> --- fs/select.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/fs/select.c b/fs/select.c index 8ed9da50896a..b99e98524fde 100644 --- a/fs/select.c +++ b/fs/select.c @@ -29,6 +29,7 @@ #include <linux/sched/rt.h> #include <linux/freezer.h> #include <net/busy_poll.h> +#include <linux/vmalloc.h> #include <asm/uaccess.h> @@ -558,6 +559,7 @@ int core_sys_select(int n, fd_set __user *inp, fd_set __user *outp, struct fdtable *fdt; /* Allocate small arguments on the stack to save memory and be faster */ long stack_fds[SELECT_STACK_ALLOC/sizeof(long)]; + unsigned long alloc_size; ret = -EINVAL; if (n < 0) @@ -580,8 +582,12 @@ int core_sys_select(int n, fd_set __user *inp, fd_set __user *outp, bits = stack_fds; if (size > sizeof(stack_fds) / 6) { /* Not enough space in on-stack array; must use kmalloc */ + alloc_size = 6 * size; ret = -ENOMEM; - bits = kmalloc(6 * size, GFP_KERNEL); + bits = kmalloc(alloc_size, GFP_KERNEL|__GFP_NOWARN); + if (!bits && alloc_size > PAGE_SIZE) + bits = vmalloc(alloc_size); + if (!bits) goto out_nofds; } @@ -618,7 +624,7 @@ int core_sys_select(int n, fd_set __user *inp, fd_set __user *outp, out: if (bits != stack_fds) - kfree(bits); + kvfree(bits); out_nofds: return ret; } -- 2.10.0
WARNING: multiple messages have this Message-ID (diff)
From: Vlastimil Babka <vbabka@suse.cz> To: Alexander Viro <viro@zeniv.linux.org.uk>, Andrew Morton <akpm@linux-foundation.org> Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Michal Hocko <mhocko@kernel.org>, netdev@vger.kernel.org, Eric Dumazet <eric.dumazet@gmail.com>, Vlastimil Babka <vbabka@suse.cz> Subject: [PATCH v2] fs/select: add vmalloc fallback for select(2) Date: Thu, 22 Sep 2016 18:43:59 +0200 [thread overview] Message-ID: <20160922164359.9035-1-vbabka@suse.cz> (raw) The select(2) syscall performs a kmalloc(size, GFP_KERNEL) where size grows with the number of fds passed. We had a customer report page allocation failures of order-4 for this allocation. This is a costly order, so it might easily fail, as the VM expects such allocation to have a lower-order fallback. Such trivial fallback is vmalloc(), as the memory doesn't have to be physically contiguous. Also the allocation is temporary for the duration of the syscall, so it's unlikely to stress vmalloc too much. Note that the poll(2) syscall seems to use a linked list of order-0 pages, so it doesn't need this kind of fallback. [eric.dumazet@gmail.com: fix failure path logic] Signed-off-by: Vlastimil Babka <vbabka@suse.cz> --- fs/select.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/fs/select.c b/fs/select.c index 8ed9da50896a..b99e98524fde 100644 --- a/fs/select.c +++ b/fs/select.c @@ -29,6 +29,7 @@ #include <linux/sched/rt.h> #include <linux/freezer.h> #include <net/busy_poll.h> +#include <linux/vmalloc.h> #include <asm/uaccess.h> @@ -558,6 +559,7 @@ int core_sys_select(int n, fd_set __user *inp, fd_set __user *outp, struct fdtable *fdt; /* Allocate small arguments on the stack to save memory and be faster */ long stack_fds[SELECT_STACK_ALLOC/sizeof(long)]; + unsigned long alloc_size; ret = -EINVAL; if (n < 0) @@ -580,8 +582,12 @@ int core_sys_select(int n, fd_set __user *inp, fd_set __user *outp, bits = stack_fds; if (size > sizeof(stack_fds) / 6) { /* Not enough space in on-stack array; must use kmalloc */ + alloc_size = 6 * size; ret = -ENOMEM; - bits = kmalloc(6 * size, GFP_KERNEL); + bits = kmalloc(alloc_size, GFP_KERNEL|__GFP_NOWARN); + if (!bits && alloc_size > PAGE_SIZE) + bits = vmalloc(alloc_size); + if (!bits) goto out_nofds; } @@ -618,7 +624,7 @@ int core_sys_select(int n, fd_set __user *inp, fd_set __user *outp, out: if (bits != stack_fds) - kfree(bits); + kvfree(bits); out_nofds: return ret; } -- 2.10.0 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next reply other threads:[~2016-09-22 16:44 UTC|newest] Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top 2016-09-22 16:43 Vlastimil Babka [this message] 2016-09-22 16:43 ` [PATCH v2] fs/select: add vmalloc fallback for select(2) Vlastimil Babka 2016-09-22 16:49 ` Eric Dumazet 2016-09-22 16:49 ` Eric Dumazet 2016-09-22 16:49 ` Eric Dumazet 2016-09-22 16:56 ` Vlastimil Babka 2016-09-22 16:56 ` Vlastimil Babka 2016-09-22 17:07 ` Eric Dumazet 2016-09-22 17:07 ` Eric Dumazet 2016-09-22 17:07 ` Eric Dumazet 2016-09-22 17:55 ` Vlastimil Babka 2016-09-22 17:55 ` Vlastimil Babka 2016-09-23 9:42 ` David Laight 2016-09-23 9:58 ` Vlastimil Babka 2016-09-23 9:58 ` Vlastimil Babka 2016-09-23 9:58 ` Vlastimil Babka 2016-09-23 13:35 ` David Laight 2016-09-26 10:01 ` Vlastimil Babka 2016-09-26 10:01 ` Vlastimil Babka 2016-09-26 15:02 ` David Laight 2016-09-25 18:50 ` Andi Kleen 2016-09-25 18:50 ` Andi Kleen 2016-09-27 0:01 ` Andrew Morton 2016-09-27 0:01 ` Andrew Morton 2016-09-27 1:38 ` Eric Dumazet 2016-09-27 1:38 ` Eric Dumazet 2016-09-27 1:38 ` Eric Dumazet 2016-09-27 8:13 ` Vlastimil Babka 2016-09-27 8:13 ` Vlastimil Babka 2016-09-27 13:34 ` Eric Dumazet 2016-09-27 13:34 ` Eric Dumazet 2016-09-27 13:34 ` Eric Dumazet 2016-09-27 8:06 ` Vlastimil Babka 2016-09-27 8:06 ` Vlastimil Babka 2016-09-27 8:45 ` [PATCH v3] " Vlastimil Babka 2016-09-27 8:45 ` Vlastimil Babka 2016-09-27 10:22 ` Michal Hocko 2016-09-27 10:22 ` Michal Hocko
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