From: Andrew Morton <akpm@linux-foundation.org>
To: willy@infradead.org,peterx@redhat.com,lukas.bulwahn@gmail.com,kirill.shutemov@linux.intel.com,jgg@ziepe.ca,jgg@nvidia.com,jack@suse.cz,imbrenda@linux.ibm.com,hch@lst.de,david@redhat.com,alex.williamson@redhat.com,aarcange@redhat.com,jhubbard@nvidia.com,akpm@linux-foundation.org,patches@lists.linux.dev,linux-mm@kvack.org,mm-commits@vger.kernel.org,torvalds@linux-foundation.org,akpm@linux-foundation.org
Subject: [patch 4/5] mm: change lookup_node() to use get_user_pages_fast()
Date: Fri, 11 Feb 2022 16:29:04 -0800 [thread overview]
Message-ID: <20220212002904.A1E5FC340EB@smtp.kernel.org> (raw)
In-Reply-To: <20220211162756.9f8e8baef81183041ccfc16f@linux-foundation.org>
From: John Hubbard <jhubbard@nvidia.com>
Subject: mm: change lookup_node() to use get_user_pages_fast()
The purpose of calling get_user_pages_locked() from lookup_node() was to
allow for unlocking the mmap_lock when reading a page from the disk during
a page fault (hidden behind VM_FAULT_RETRY). The idea was to reduce
contention on the heavily-used mmap_lock. (Thanks to Jan Kara for clearly
pointing that out, and in fact I've used some of his wording here.)
However, it is unlikely for lookup_node() to take a page fault. With that
in mind, change over to calling get_user_pages_fast(). This simplifies
the code, runs a little faster in the expected case, and allows removing
get_user_pages_locked() entirely, in a subsequent patch.
Link: https://lkml.kernel.org/r/20220204020010.68930-5-jhubbard@nvidia.com
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: Alex Williamson <alex.williamson@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Peter Xu <peterx@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
--- a/mm/mempolicy.c~mm-change-lookup_node-to-use-get_user_pages_fast
+++ a/mm/mempolicy.c
@@ -907,17 +907,14 @@ static void get_policy_nodemask(struct m
static int lookup_node(struct mm_struct *mm, unsigned long addr)
{
struct page *p = NULL;
- int err;
+ int ret;
- int locked = 1;
- err = get_user_pages_locked(addr & PAGE_MASK, 1, 0, &p, &locked);
- if (err > 0) {
- err = page_to_nid(p);
+ ret = get_user_pages_fast(addr & PAGE_MASK, 1, 0, &p);
+ if (ret > 0) {
+ ret = page_to_nid(p);
put_page(p);
}
- if (locked)
- mmap_read_unlock(mm);
- return err;
+ return ret;
}
/* Retrieve NUMA policy */
@@ -968,14 +965,14 @@ static long do_get_mempolicy(int *policy
if (flags & MPOL_F_NODE) {
if (flags & MPOL_F_ADDR) {
/*
- * Take a refcount on the mpol, lookup_node()
- * will drop the mmap_lock, so after calling
- * lookup_node() only "pol" remains valid, "vma"
- * is stale.
+ * Take a refcount on the mpol, because we are about to
+ * drop the mmap_lock, after which only "pol" remains
+ * valid, "vma" is stale.
*/
pol_refcount = pol;
vma = NULL;
mpol_get(pol);
+ mmap_read_unlock(mm);
err = lookup_node(mm, addr);
if (err < 0)
goto out;
_
next prev parent reply other threads:[~2022-02-12 0:29 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-12 0:27 incoming Andrew Morton
2022-02-12 0:28 ` [patch 1/5] mm: fix invalid page pointer returned with FOLL_PIN gups Andrew Morton
2022-02-12 0:32 ` Andrew Morton
2022-02-12 0:28 ` [patch 2/5] mm/gup: follow_pfn_pte(): -EEXIST cleanup Andrew Morton
2022-02-12 0:29 ` [patch 3/5] mm/gup: remove unused pin_user_pages_locked() Andrew Morton
2022-02-12 0:29 ` Andrew Morton [this message]
2022-02-12 0:29 ` [patch 5/5] mm/gup: remove unused get_user_pages_locked() Andrew Morton
2022-02-12 0:32 ` [patch 1/5] fs/binfmt_elf: fix PT_LOAD p_align values for loaders Andrew Morton
2022-02-12 0:32 ` [patch 2/5] fs/proc: task_mmu.c: don't read mapcount for migration entry Andrew Morton
2022-02-12 0:32 ` [patch 3/5] mm: vmscan: remove deadlock due to throttling failing to make progress Andrew Morton
2022-02-12 0:32 ` [patch 4/5] mm: memcg: synchronize objcg lists with a dedicated spinlock Andrew Morton
2022-02-12 0:32 ` [patch 5/5] kfence: make test case compatible with run time set sample interval Andrew Morton
2022-02-12 2:02 ` incoming Linus Torvalds
2022-02-12 5:24 ` incoming Andrew Morton
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