| Message ID | 20210823120645.8223-1-david@redhat.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [v3] madvise.2: Document MADV_POPULATE_READ and MADV_POPULATE_WRITE | expand |
On 23.08.21 14:06, David Hildenbrand wrote: > 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: Alejandro Colomar <alx.manpages@gmail.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> > --- > > v2 -> v3: > - Refine what "populating readable/writable" means > - Compare each version with MAP_POPULATE and give an example use case > - Reword SIGBUS handling > - Reword comment regarding special mappings and also add memfd_secret(2) > - Reference MADV_HWPOISON when talking about HW poisoned pages > - Minor cosmetic fixes > > v1 -> v2: > - Use semantic newlines in all cases > - Add two missing " > - Document -EFAULT handling > - Rephrase some parts to make it more generic: VM_PFNMAP and VM_IO are only > examples for special mappings > > --- > man2/madvise.2 | 156 +++++++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 156 insertions(+) > > 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), > Gentle ping.
Hi David, On 9/28/21 6:34 PM, David Hildenbrand wrote: > On 23.08.21 14:06, David Hildenbrand wrote: >> 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: Alejandro Colomar <alx.manpages@gmail.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> >> --- Patch applied. Thanks, Alex >> >> v2 -> v3: >> - Refine what "populating readable/writable" means >> - Compare each version with MAP_POPULATE and give an example use case >> - Reword SIGBUS handling >> - Reword comment regarding special mappings and also add memfd_secret(2) >> - Reference MADV_HWPOISON when talking about HW poisoned pages >> - Minor cosmetic fixes >> >> v1 -> v2: >> - Use semantic newlines in all cases >> - Add two missing " >> - Document -EFAULT handling >> - Rephrase some parts to make it more generic: VM_PFNMAP and VM_IO are >> only >> examples for special mappings >> >> --- >> man2/madvise.2 | 156 +++++++++++++++++++++++++++++++++++++++++++++++++ >> 1 file changed, 156 insertions(+) >> >> 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), >> > > Gentle ping. >
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),
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: Alejandro Colomar <alx.manpages@gmail.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> --- v2 -> v3: - Refine what "populating readable/writable" means - Compare each version with MAP_POPULATE and give an example use case - Reword SIGBUS handling - Reword comment regarding special mappings and also add memfd_secret(2) - Reference MADV_HWPOISON when talking about HW poisoned pages - Minor cosmetic fixes v1 -> v2: - Use semantic newlines in all cases - Add two missing " - Document -EFAULT handling - Rephrase some parts to make it more generic: VM_PFNMAP and VM_IO are only examples for special mappings --- man2/madvise.2 | 156 +++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 156 insertions(+)