| Message ID | 1580757507-120233-1-git-send-email-yang.shi@linux.alibaba.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v3] move_pages.2: Returning positive value is a new error case | expand |
On Tue 04-02-20 03:18:27, Yang Shi wrote: > Since commit a49bd4d71637 ("mm, numa: rework do_pages_move"), > the semantic of move_pages() has changed to return the number of > non-migrated pages if they were result of a non-fatal reasons (usually a > busy page). This was an unintentional change that hasn't been noticed > except for LTP tests which checked for the documented behavior. > > There are two ways to go around this change. We can even get back to the > original behavior and return -EAGAIN whenever migrate_pages is not able > to migrate pages due to non-fatal reasons. Another option would be to > simply continue with the changed semantic and extend move_pages > documentation to clarify that -errno is returned on an invalid input or > when migration simply cannot succeed (e.g. -ENOMEM, -EBUSY) or the > number of pages that couldn't have been migrated due to ephemeral > reasons (e.g. page is pinned or locked for other reasons). > > We decided to keep the second option in kernel because this behavior is in > place for some time without anybody complaining and possibly new users > depending on it. Also it allows to have a slightly easier error handling > as the caller knows that it is worth to retry when err > 0. > > Update man pages to reflect the new semantic. > > Cc: Michal Hocko <mhocko@suse.com> > Cc: Michael Kerrisk <mtk.manpages@gmail.com> > Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com> Acked-by: Michal Hocko <mhocko@suse.com> > --- > v3: * Fixed the comments from David Hildenbrand. > * Fixed the inaccuracy about pre-initialized status array values. > v2: * Added notes about status array per Michal. > * Added Michal's Acked-by. > > man2/move_pages.2 | 10 ++++++++-- > 1 file changed, 8 insertions(+), 2 deletions(-) > > diff --git a/man2/move_pages.2 b/man2/move_pages.2 > index 1bf1053..50c83a4 100644 > --- a/man2/move_pages.2 > +++ b/man2/move_pages.2 > @@ -104,7 +104,9 @@ pages that need to be moved. > is an array of integers that return the status of each page. > The array contains valid values only if > .BR move_pages () > -did not return an error. > +did not return an error. Pre-initialization of the array to the value > +which cannot represent a real numa node or valid error of status array > +could help to identify pages that have been migrated > .PP > .I flags > specify what types of pages to move. > @@ -164,9 +166,13 @@ returns zero. > .\" do the right thing? > On error, it returns \-1, and sets > .I errno > -to indicate the error. > +to indicate the error. If positive value is returned, it is the number of > +non-migrated pages. > .SH ERRORS > .TP > +.B Positive value > +The number of non-migrated pages if they were the result of non-fatal > +reasons (since version 4.17). > .B E2BIG > Too many pages to move. > Since Linux 2.6.29, > -- > 1.8.3.1
On 2/10/20 1:36 AM, Michal Hocko wrote: > On Tue 04-02-20 03:18:27, Yang Shi wrote: >> Since commit a49bd4d71637 ("mm, numa: rework do_pages_move"), >> the semantic of move_pages() has changed to return the number of >> non-migrated pages if they were result of a non-fatal reasons (usually a >> busy page). This was an unintentional change that hasn't been noticed >> except for LTP tests which checked for the documented behavior. >> >> There are two ways to go around this change. We can even get back to the >> original behavior and return -EAGAIN whenever migrate_pages is not able >> to migrate pages due to non-fatal reasons. Another option would be to >> simply continue with the changed semantic and extend move_pages >> documentation to clarify that -errno is returned on an invalid input or >> when migration simply cannot succeed (e.g. -ENOMEM, -EBUSY) or the >> number of pages that couldn't have been migrated due to ephemeral >> reasons (e.g. page is pinned or locked for other reasons). >> >> We decided to keep the second option in kernel because this behavior is in >> place for some time without anybody complaining and possibly new users >> depending on it. Also it allows to have a slightly easier error handling >> as the caller knows that it is worth to retry when err > 0. >> >> Update man pages to reflect the new semantic. >> >> Cc: Michal Hocko <mhocko@suse.com> >> Cc: Michael Kerrisk <mtk.manpages@gmail.com> >> Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com> Hi Michael, Would you please consider take this patch? The kernel change has been upstreamed. Thanks, Yang > Acked-by: Michal Hocko <mhocko@suse.com> > >> --- >> v3: * Fixed the comments from David Hildenbrand. >> * Fixed the inaccuracy about pre-initialized status array values. >> v2: * Added notes about status array per Michal. >> * Added Michal's Acked-by. >> >> man2/move_pages.2 | 10 ++++++++-- >> 1 file changed, 8 insertions(+), 2 deletions(-) >> >> diff --git a/man2/move_pages.2 b/man2/move_pages.2 >> index 1bf1053..50c83a4 100644 >> --- a/man2/move_pages.2 >> +++ b/man2/move_pages.2 >> @@ -104,7 +104,9 @@ pages that need to be moved. >> is an array of integers that return the status of each page. >> The array contains valid values only if >> .BR move_pages () >> -did not return an error. >> +did not return an error. Pre-initialization of the array to the value >> +which cannot represent a real numa node or valid error of status array >> +could help to identify pages that have been migrated >> .PP >> .I flags >> specify what types of pages to move. >> @@ -164,9 +166,13 @@ returns zero. >> .\" do the right thing? >> On error, it returns \-1, and sets >> .I errno >> -to indicate the error. >> +to indicate the error. If positive value is returned, it is the number of >> +non-migrated pages. >> .SH ERRORS >> .TP >> +.B Positive value >> +The number of non-migrated pages if they were the result of non-fatal >> +reasons (since version 4.17). >> .B E2BIG >> Too many pages to move. >> Since Linux 2.6.29, >> -- >> 1.8.3.1
On Thu, Feb 20, 2020 at 9:07 AM Yang Shi <yang.shi@linux.alibaba.com> wrote: > > > > On 2/10/20 1:36 AM, Michal Hocko wrote: > > On Tue 04-02-20 03:18:27, Yang Shi wrote: > >> Since commit a49bd4d71637 ("mm, numa: rework do_pages_move"), > >> the semantic of move_pages() has changed to return the number of > >> non-migrated pages if they were result of a non-fatal reasons (usually a > >> busy page). This was an unintentional change that hasn't been noticed > >> except for LTP tests which checked for the documented behavior. > >> > >> There are two ways to go around this change. We can even get back to the > >> original behavior and return -EAGAIN whenever migrate_pages is not able > >> to migrate pages due to non-fatal reasons. Another option would be to > >> simply continue with the changed semantic and extend move_pages > >> documentation to clarify that -errno is returned on an invalid input or > >> when migration simply cannot succeed (e.g. -ENOMEM, -EBUSY) or the > >> number of pages that couldn't have been migrated due to ephemeral > >> reasons (e.g. page is pinned or locked for other reasons). > >> > >> We decided to keep the second option in kernel because this behavior is in > >> place for some time without anybody complaining and possibly new users > >> depending on it. Also it allows to have a slightly easier error handling > >> as the caller knows that it is worth to retry when err > 0. > >> > >> Update man pages to reflect the new semantic. > >> > >> Cc: Michal Hocko <mhocko@suse.com> > >> Cc: Michael Kerrisk <mtk.manpages@gmail.com> > >> Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com> > Hi Michale, Maybe my work email went to your spam folder. So, ping with my personal email. Would you please consider take this patch? Thanks, Yang > Hi Michael, > > Would you please consider take this patch? The kernel change has been > upstreamed. > > Thanks, > Yang > > > Acked-by: Michal Hocko <mhocko@suse.com> > > > >> --- > >> v3: * Fixed the comments from David Hildenbrand. > >> * Fixed the inaccuracy about pre-initialized status array values. > >> v2: * Added notes about status array per Michal. > >> * Added Michal's Acked-by. > >> > >> man2/move_pages.2 | 10 ++++++++-- > >> 1 file changed, 8 insertions(+), 2 deletions(-) > >> > >> diff --git a/man2/move_pages.2 b/man2/move_pages.2 > >> index 1bf1053..50c83a4 100644 > >> --- a/man2/move_pages.2 > >> +++ b/man2/move_pages.2 > >> @@ -104,7 +104,9 @@ pages that need to be moved. > >> is an array of integers that return the status of each page. > >> The array contains valid values only if > >> .BR move_pages () > >> -did not return an error. > >> +did not return an error. Pre-initialization of the array to the value > >> +which cannot represent a real numa node or valid error of status array > >> +could help to identify pages that have been migrated > >> .PP > >> .I flags > >> specify what types of pages to move. > >> @@ -164,9 +166,13 @@ returns zero. > >> .\" do the right thing? > >> On error, it returns \-1, and sets > >> .I errno > >> -to indicate the error. > >> +to indicate the error. If positive value is returned, it is the number of > >> +non-migrated pages. > >> .SH ERRORS > >> .TP > >> +.B Positive value > >> +The number of non-migrated pages if they were the result of non-fatal > >> +reasons (since version 4.17). > >> .B E2BIG > >> Too many pages to move. > >> Since Linux 2.6.29, > >> -- > >> 1.8.3.1 >
Hello Yang Shi, On 2/3/20 8:18 PM, Yang Shi wrote: > Since commit a49bd4d71637 ("mm, numa: rework do_pages_move"), > the semantic of move_pages() has changed to return the number of > non-migrated pages if they were result of a non-fatal reasons (usually a > busy page). This was an unintentional change that hasn't been noticed > except for LTP tests which checked for the documented behavior. > > There are two ways to go around this change. We can even get back to the > original behavior and return -EAGAIN whenever migrate_pages is not able > to migrate pages due to non-fatal reasons. Another option would be to > simply continue with the changed semantic and extend move_pages > documentation to clarify that -errno is returned on an invalid input or > when migration simply cannot succeed (e.g. -ENOMEM, -EBUSY) or the > number of pages that couldn't have been migrated due to ephemeral > reasons (e.g. page is pinned or locked for other reasons). > > We decided to keep the second option in kernel because this behavior is in > place for some time without anybody complaining and possibly new users > depending on it. Also it allows to have a slightly easier error handling > as the caller knows that it is worth to retry when err > 0. > > Update man pages to reflect the new semantic. Thanks for the patch. I've applied it. @Michal: thanks for the Ack. Cheers, Michael > > Cc: Michal Hocko <mhocko@suse.com> > Cc: Michael Kerrisk <mtk.manpages@gmail.com> > Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com> > --- > v3: * Fixed the comments from David Hildenbrand. > * Fixed the inaccuracy about pre-initialized status array values. > v2: * Added notes about status array per Michal. > * Added Michal's Acked-by. > > man2/move_pages.2 | 10 ++++++++-- > 1 file changed, 8 insertions(+), 2 deletions(-) > > diff --git a/man2/move_pages.2 b/man2/move_pages.2 > index 1bf1053..50c83a4 100644 > --- a/man2/move_pages.2 > +++ b/man2/move_pages.2 > @@ -104,7 +104,9 @@ pages that need to be moved. > is an array of integers that return the status of each page. > The array contains valid values only if > .BR move_pages () > -did not return an error. > +did not return an error. Pre-initialization of the array to the value > +which cannot represent a real numa node or valid error of status array > +could help to identify pages that have been migrated > .PP > .I flags > specify what types of pages to move. > @@ -164,9 +166,13 @@ returns zero. > .\" do the right thing? > On error, it returns \-1, and sets > .I errno > -to indicate the error. > +to indicate the error. If positive value is returned, it is the number of > +non-migrated pages. > .SH ERRORS > .TP > +.B Positive value > +The number of non-migrated pages if they were the result of non-fatal > +reasons (since version 4.17). > .B E2BIG > Too many pages to move. > Since Linux 2.6.29, >
diff --git a/man2/move_pages.2 b/man2/move_pages.2 index 1bf1053..50c83a4 100644 --- a/man2/move_pages.2 +++ b/man2/move_pages.2 @@ -104,7 +104,9 @@ pages that need to be moved. is an array of integers that return the status of each page. The array contains valid values only if .BR move_pages () -did not return an error. +did not return an error. Pre-initialization of the array to the value +which cannot represent a real numa node or valid error of status array +could help to identify pages that have been migrated .PP .I flags specify what types of pages to move. @@ -164,9 +166,13 @@ returns zero. .\" do the right thing? On error, it returns \-1, and sets .I errno -to indicate the error. +to indicate the error. If positive value is returned, it is the number of +non-migrated pages. .SH ERRORS .TP +.B Positive value +The number of non-migrated pages if they were the result of non-fatal +reasons (since version 4.17). .B E2BIG Too many pages to move. Since Linux 2.6.29,
Since commit a49bd4d71637 ("mm, numa: rework do_pages_move"), the semantic of move_pages() has changed to return the number of non-migrated pages if they were result of a non-fatal reasons (usually a busy page). This was an unintentional change that hasn't been noticed except for LTP tests which checked for the documented behavior. There are two ways to go around this change. We can even get back to the original behavior and return -EAGAIN whenever migrate_pages is not able to migrate pages due to non-fatal reasons. Another option would be to simply continue with the changed semantic and extend move_pages documentation to clarify that -errno is returned on an invalid input or when migration simply cannot succeed (e.g. -ENOMEM, -EBUSY) or the number of pages that couldn't have been migrated due to ephemeral reasons (e.g. page is pinned or locked for other reasons). We decided to keep the second option in kernel because this behavior is in place for some time without anybody complaining and possibly new users depending on it. Also it allows to have a slightly easier error handling as the caller knows that it is worth to retry when err > 0. Update man pages to reflect the new semantic. Cc: Michal Hocko <mhocko@suse.com> Cc: Michael Kerrisk <mtk.manpages@gmail.com> Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com> --- v3: * Fixed the comments from David Hildenbrand. * Fixed the inaccuracy about pre-initialized status array values. v2: * Added notes about status array per Michal. * Added Michal's Acked-by. man2/move_pages.2 | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-)