From def5efe0376501ef7bd6b53ed061512c142e59aa Mon Sep 17 00:00:00 2001 From: David Rientjes Date: Fri, 24 Feb 2017 14:58:47 -0800 Subject: mm, madvise: fail with ENOMEM when splitting vma will hit max_map_count If madvise(2) advice will result in the underlying vma being split and the number of areas mapped by the process will exceed /proc/sys/vm/max_map_count as a result, return ENOMEM instead of EAGAIN. EAGAIN is returned by madvise(2) when a kernel resource, such as slab, is temporarily unavailable. It indicates that userspace should retry the advice in the near future. This is important for advice such as MADV_DONTNEED which is often used by malloc implementations to free memory back to the system: we really do want to free memory back when madvise(2) returns EAGAIN because slab allocations (for vmas, anon_vmas, or mempolicies) cannot be allocated. Encountering /proc/sys/vm/max_map_count is not a temporary failure, however, so return ENOMEM to indicate this is a more serious issue. A followup patch to the man page will specify this behavior. Link: http://lkml.kernel.org/r/alpine.DEB.2.10.1701241431120.42507@chino.kir.corp.google.com Signed-off-by: David Rientjes Cc: Jonathan Corbet Cc: Johannes Weiner Cc: Jerome Marchand Cc: "Kirill A. Shutemov" Cc: Michael Kerrisk Cc: Anshuman Khandual Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Documentation/sysctl/vm.txt | 4 ++-- Documentation/vm/ksm.txt | 4 ++++ 2 files changed, 6 insertions(+), 2 deletions(-) (limited to 'Documentation') diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt index 95ccbe6d79ce..b4ad97f10b8e 100644 --- a/Documentation/sysctl/vm.txt +++ b/Documentation/sysctl/vm.txt @@ -376,8 +376,8 @@ max_map_count: This file contains the maximum number of memory map areas a process may have. Memory map areas are used as a side-effect of calling -malloc, directly by mmap and mprotect, and also when loading shared -libraries. +malloc, directly by mmap, mprotect, and madvise, and also when loading +shared libraries. While most applications need less than a thousand maps, certain programs, particularly malloc debuggers, may consume lots of them, diff --git a/Documentation/vm/ksm.txt b/Documentation/vm/ksm.txt index 0c64a81d6808..6b0ca7feb135 100644 --- a/Documentation/vm/ksm.txt +++ b/Documentation/vm/ksm.txt @@ -38,6 +38,10 @@ the range for whenever the KSM daemon is started; even if the range cannot contain any pages which KSM could actually merge; even if MADV_UNMERGEABLE is applied to a range which was never MADV_MERGEABLE. +If a region of memory must be split into at least one new MADV_MERGEABLE +or MADV_UNMERGEABLE region, the madvise may return ENOMEM if the process +will exceed vm.max_map_count (see Documentation/sysctl/vm.txt). + Like other madvise calls, they are intended for use on mapped areas of the user address space: they will report ENOMEM if the specified range includes unmapped gaps (though working on the intervening mapped areas), -- cgit v1.2.3