diff options
author | David Hildenbrand <david@redhat.com> | 2021-08-23 14:06:45 +0200 |
---|---|---|
committer | Alejandro Colomar <alx.manpages@gmail.com> | 2021-10-02 20:11:45 +0200 |
commit | 9f307c06efc8c40a8aff30cf13ef3a8528be9222 (patch) | |
tree | fdfa4b5b04f44d6b620b04e33a6c0ff20f22eb66 /man2/madvise.2 | |
parent | a1426ea9a8c3fcda367c7cb74db4be87bafba07c (diff) |
madvise.2: Document MADV_POPULATE_READ and MADV_POPULATE_WRITE
MADV_POPULATE_READ and MADV_POPULATE_WRITE have been merged into
upstream Linux via commit 4ca9b3859dac ("mm/madvise: introduce
MADV_POPULATE_(READ|WRITE) to prefault page tables"), part of v5.14-rc1.
Further, commit eb2faa513c24 ("mm/madvise: report SIGBUS as -EFAULT for
MADV_POPULATE_(READ|WRITE)"), part of v5.14-rc6, made sure that SIGBUS is
converted to -EFAULT instead of -EINVAL.
Let's document the behavior and error conditions of these new madvise()
options.
Acked-by: Pankaj Gupta <pankaj.gupta@ionos.com>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Jann Horn <jannh@google.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Linux API <linux-api@vger.kernel.org>
Cc: linux-mm@kvack.org
Signed-off-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Alejandro Colomar <alx.manpages@gmail.com>
Diffstat (limited to 'man2/madvise.2')
-rw-r--r-- | man2/madvise.2 | 156 |
1 files changed, 156 insertions, 0 deletions
diff --git a/man2/madvise.2 b/man2/madvise.2 index f1f384c0c..37f6dd6fa 100644 --- a/man2/madvise.2 +++ b/man2/madvise.2 @@ -469,6 +469,106 @@ If a page is file-backed and dirty, it will be written back to the backing storage. The advice might be ignored for some pages in the range when it is not applicable. +.TP +.BR MADV_POPULATE_READ " (since Linux 5.14)" +"Populate (prefault) page tables readable, +faulting in all pages in the range just as if manually reading from each page; +however, +avoid the actual memory access that would have been performed after handling +the fault. +.IP +In contrast to +.BR MAP_POPULATE , +.B MADV_POPULATE_READ +does not hide errors, +can be applied to (parts of) existing mappings and will always populate +(prefault) page tables readable. +One example use case is prefaulting a file mapping, +reading all file content from disk; +however, +pages won't be dirtied and consequently won't have to be written back to disk +when evicting the pages from memory. +.IP +Depending on the underlying mapping, +map the shared zeropage, +preallocate memory or read the underlying file; +files with holes might or might not preallocate blocks. +If populating fails, +a +.B SIGBUS +signal is not generated; instead, an error is returned. +.IP +If +.B MADV_POPULATE_READ +succeeds, +all page tables have been populated (prefaulted) readable once. +If +.B MADV_POPULATE_READ +fails, +some page tables might have been populated. +.IP +.B MADV_POPULATE_READ +cannot be applied to mappings without read permissions +and special mappings, +for example, +mappings marked with kernel-internal flags such as +.B VM_PFNMAP +or +.BR VM_IO , +or secret memory regions created using +.BR memfd_secret(2) . +.IP +Note that with +.BR MADV_POPULATE_READ , +the process can be killed at any moment when the system runs out of memory. +.TP +.BR MADV_POPULATE_WRITE " (since Linux 5.14)" +Populate (prefault) page tables writable, +faulting in all pages in the range just as if manually writing to each +each page; +however, +avoid the actual memory access that would have been performed after handling +the fault. +.IP +In contrast to +.BR MAP_POPULATE , +MADV_POPULATE_WRITE does not hide errors, +can be applied to (parts of) existing mappings and will always populate +(prefault) page tables writable. +One example use case is preallocating memory, +breaking any CoW (Copy on Write). +.IP +Depending on the underlying mapping, +preallocate memory or read the underlying file; +files with holes will preallocate blocks. +If populating fails, +a +.B SIGBUS +signal is not generated; instead, an error is returned. +.IP +If +.B MADV_POPULATE_WRITE +succeeds, +all page tables have been populated (prefaulted) writable once. +If +.B MADV_POPULATE_WRITE +fails, +some page tables might have been populated. +.IP +.B MADV_POPULATE_WRITE +cannot be applied to mappings without write permissions +and special mappings, +for example, +mappings marked with kernel-internal flags such as +.B VM_PFNMAP +or +.BR VM_IO , +or secret memory regions created using +.BR memfd_secret(2) . +.IP +Note that with +.BR MADV_POPULATE_WRITE , +the process can be killed at any moment when the system runs out of memory. .SH RETURN VALUE On success, .BR madvise () @@ -490,6 +590,22 @@ A kernel resource was temporarily unavailable. .B EBADF The map exists, but the area maps something that isn't a file. .TP +.B EFAULT +.I advice +is +.B MADV_POPULATE_READ +or +.BR MADV_POPULATE_WRITE , +and populating (prefaulting) page tables failed because a +.B SIGBUS +would have been generated on actual memory access and the reason is not a +HW poisoned page +(HW poisoned pages can, +for example, +be created using the +.B MADV_HWPOISON +flag described elsewhere in this page). +.TP .B EINVAL .I addr is not page-aligned or @@ -533,6 +649,22 @@ or .BR VM_PFNMAP ranges. .TP +.B EINVAL +.I advice +is +.B MADV_POPULATE_READ +or +.BR MADV_POPULATE_WRITE , +but the specified address range includes ranges with insufficient permissions +or special mappings, +for example, +mappings marked with kernel-internal flags such a +.B VM_IO +or +.BR VM_PFNMAP , +or secret memory regions created using +.BR memfd_secret(2) . +.TP .B EIO (for .BR MADV_WILLNEED ) @@ -548,6 +680,15 @@ Not enough memory: paging in failed. Addresses in the specified range are not currently mapped, or are outside the address space of the process. .TP +.B ENOMEM +.I advice +is +.B MADV_POPULATE_READ +or +.BR MADV_POPULATE_WRITE , +and populating (prefaulting) page tables failed because there was not enough +memory. +.TP .B EPERM .I advice is @@ -555,6 +696,20 @@ is but the caller does not have the .B CAP_SYS_ADMIN capability. +.TP +.B EHWPOISON +.I advice +is +.B MADV_POPULATE_READ +or +.BR MADV_POPULATE_WRITE , +and populating (prefaulting) page tables failed because a HW poisoned page +(HW poisoned pages can, +for example, +be created using the +.B MADV_HWPOISON +flag described elsewhere in this page) +was encountered. .SH VERSIONS Since Linux 3.18, .\" commit d3ac21cacc24790eb45d735769f35753f5b56ceb @@ -602,6 +757,7 @@ from the system call, as it should). .\" function first appeared in 4.4BSD. .SH SEE ALSO .BR getrlimit (2), +.BR memfd_secret(2), .BR mincore (2), .BR mmap (2), .BR mprotect (2), |