| Message ID | 20201019083632.25417-1-yanfei.xu@windriver.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2] mm/compaction: Rename 'start_pfn' to 'iteration_start_pfn' in compact_zone() | expand |
> From: Yanfei Xu <yanfei.xu@windriver.com> > > There are two 'start_pfn' declared in compact_zone() which have > different meaning. Rename the second one to 'iteration_start_pfn' > to prevent trace_mm_compaction_end() from tracing an undesirable > value. > > BTW, remove an useless semicolon. > > Acked-by: David Hildenbrand <david@redhat.com> > Acked-by: Vlastimil Babka <vbabka@suse.cz> > Signed-off-by: Yanfei Xu <yanfei.xu@windriver.com> > --- > v1->v2: > Rename 'start_pfn' to 'iteration_start_pfn' and change commit messages. > > mm/compaction.c | 7 +++---- > 1 file changed, 3 insertions(+), 4 deletions(-) > > diff --git a/mm/compaction.c b/mm/compaction.c > index 176dcded298e..ccd27c739fd6 100644 > --- a/mm/compaction.c > +++ b/mm/compaction.c > @@ -2272,7 +2272,7 @@ compact_zone(struct compact_control *cc, struct capture_control *capc) > > while ((ret = compact_finished(cc)) == COMPACT_CONTINUE) { > int err; > - unsigned long start_pfn = cc->migrate_pfn; > + unsigned long iteration_start_pfn = cc->migrate_pfn; > > /* > * Avoid multiple rescans which can happen if a page cannot be > @@ -2284,7 +2284,7 @@ compact_zone(struct compact_control *cc, struct capture_control *capc) > */ > cc->rescan = false; > if (pageblock_start_pfn(last_migrated_pfn) == > - pageblock_start_pfn(start_pfn)) { > + pageblock_start_pfn(iteration_start_pfn)) { > cc->rescan = true; > } > > @@ -2308,8 +2308,7 @@ compact_zone(struct compact_control *cc, struct capture_control *capc) > goto check_drain; > case ISOLATE_SUCCESS: > update_cached = false; > - last_migrated_pfn = start_pfn; > - ; > + last_migrated_pfn = iteration_start_pfn; > } > > err = migrate_pages(&cc->migratepages, compaction_alloc, Improves readability. Acked-by: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
On 10/19/20 10:36 AM, yanfei.xu@windriver.com wrote: > From: Yanfei Xu <yanfei.xu@windriver.com> > > There are two 'start_pfn' declared in compact_zone() which have > different meaning. Rename the second one to 'iteration_start_pfn' > to prevent trace_mm_compaction_end() from tracing an undesirable > value. "to prevent confusion.", because trace_mm_compaction_end() has the correct value even before the patch - the second start_pfn is out of scope at that point. Thanks > BTW, remove an useless semicolon. > > Acked-by: David Hildenbrand <david@redhat.com> > Acked-by: Vlastimil Babka <vbabka@suse.cz> > Signed-off-by: Yanfei Xu <yanfei.xu@windriver.com> > --- > v1->v2: > Rename 'start_pfn' to 'iteration_start_pfn' and change commit messages. > > mm/compaction.c | 7 +++---- > 1 file changed, 3 insertions(+), 4 deletions(-) > > diff --git a/mm/compaction.c b/mm/compaction.c > index 176dcded298e..ccd27c739fd6 100644 > --- a/mm/compaction.c > +++ b/mm/compaction.c > @@ -2272,7 +2272,7 @@ compact_zone(struct compact_control *cc, struct capture_control *capc) > > while ((ret = compact_finished(cc)) == COMPACT_CONTINUE) { > int err; > - unsigned long start_pfn = cc->migrate_pfn; > + unsigned long iteration_start_pfn = cc->migrate_pfn; > > /* > * Avoid multiple rescans which can happen if a page cannot be > @@ -2284,7 +2284,7 @@ compact_zone(struct compact_control *cc, struct capture_control *capc) > */ > cc->rescan = false; > if (pageblock_start_pfn(last_migrated_pfn) == > - pageblock_start_pfn(start_pfn)) { > + pageblock_start_pfn(iteration_start_pfn)) { > cc->rescan = true; > } > > @@ -2308,8 +2308,7 @@ compact_zone(struct compact_control *cc, struct capture_control *capc) > goto check_drain; > case ISOLATE_SUCCESS: > update_cached = false; > - last_migrated_pfn = start_pfn; > - ; > + last_migrated_pfn = iteration_start_pfn; > } > > err = migrate_pages(&cc->migratepages, compaction_alloc, >
On 10/19/20 5:40 PM, Vlastimil Babka wrote: > On 10/19/20 10:36 AM, yanfei.xu@windriver.com wrote: >> From: Yanfei Xu <yanfei.xu@windriver.com> >> >> There are two 'start_pfn' declared in compact_zone() which have >> different meaning. Rename the second one to 'iteration_start_pfn' >> to prevent trace_mm_compaction_end() from tracing an undesirable >> value. > > "to prevent confusion.", because trace_mm_compaction_end() has the > correct value even before the patch - the second start_pfn is out > of scope at that point. > > Thanks > In the while-statement, the second start_pfn is always be reassigned the value of cc->migrate_pfn in every loop, also the cc->migrate_pfn might be changed in the loop. Does trace_mm_compaction_end() really want to trace the new assinged start_pfn? Without the patch： 566e54e11（mm, compaction: remove last_migrated_pfn from compact_control）, there is only one start_pfn which has a fixed value. The trace_mm_compaction_end() trace it too. Thus, I think the tracepoint might get an undesireble value.:) Thanks, Yanfei >> BTW, remove an useless semicolon. >> >> Acked-by: David Hildenbrand <david@redhat.com> >> Acked-by: Vlastimil Babka <vbabka@suse.cz> >> Signed-off-by: Yanfei Xu <yanfei.xu@windriver.com> >> --- >> v1->v2: >> Rename 'start_pfn' to 'iteration_start_pfn' and change commit messages. >> >> mm/compaction.c | 7 +++---- >> 1 file changed, 3 insertions(+), 4 deletions(-) >> >> diff --git a/mm/compaction.c b/mm/compaction.c >> index 176dcded298e..ccd27c739fd6 100644 >> --- a/mm/compaction.c >> +++ b/mm/compaction.c >> @@ -2272,7 +2272,7 @@ compact_zone(struct compact_control *cc, struct >> capture_control *capc) >> while ((ret = compact_finished(cc)) == COMPACT_CONTINUE) { >> int err; >> - unsigned long start_pfn = cc->migrate_pfn; >> + unsigned long iteration_start_pfn = cc->migrate_pfn; >> /* >> * Avoid multiple rescans which can happen if a page cannot be >> @@ -2284,7 +2284,7 @@ compact_zone(struct compact_control *cc, struct >> capture_control *capc) >> */ >> cc->rescan = false; >> if (pageblock_start_pfn(last_migrated_pfn) == >> - pageblock_start_pfn(start_pfn)) { >> + pageblock_start_pfn(iteration_start_pfn)) { >> cc->rescan = true; >> } >> @@ -2308,8 +2308,7 @@ compact_zone(struct compact_control *cc, struct >> capture_control *capc) >> goto check_drain; >> case ISOLATE_SUCCESS: >> update_cached = false; >> - last_migrated_pfn = start_pfn; >> - ; >> + last_migrated_pfn = iteration_start_pfn; >> } >> err = migrate_pages(&cc->migratepages, compaction_alloc, >> > >
On 10/19/20 12:29 PM, Xu, Yanfei wrote: > > > On 10/19/20 5:40 PM, Vlastimil Babka wrote: >> On 10/19/20 10:36 AM, yanfei.xu@windriver.com wrote: >>> From: Yanfei Xu <yanfei.xu@windriver.com> >>> >>> There are two 'start_pfn' declared in compact_zone() which have >>> different meaning. Rename the second one to 'iteration_start_pfn' >>> to prevent trace_mm_compaction_end() from tracing an undesirable >>> value. >> >> "to prevent confusion.", because trace_mm_compaction_end() has the >> correct value even before the patch - the second start_pfn is out >> of scope at that point. >> >> Thanks >> > In the while-statement, the second start_pfn is always be reassigned the > value of cc->migrate_pfn in every loop, also the cc->migrate_pfn might > be changed in the loop. Does trace_mm_compaction_end() really want to > trace the new assinged start_pfn? compact_zone() { unsigned long start_pfn = cc->zone->zone_start_pfn; while ((ret = compact_finished(cc)) == COMPACT_CONTINUE) { unsigned long start_pfn = cc->migrate_pfn; ... } trace_mm_compaction_end(start_pfn, cc->migrate_pfn, ...) } Unless my C knowledge fails me completely, the start_pfn in the while loop is a new different local variable that shadows the start_pfn from compact_zone() level, but does not modify its value. After while loop finishes, start_pfn has still the value assigned at compact_zone() beginning and that's what tracepoint sees. So renaming the variable in while loop is not a bug fix, but removing confusion. > Without the patch： 566e54e11（mm, compaction: remove last_migrated_pfn > from compact_control）, there is only one start_pfn which has a fixed > value. The trace_mm_compaction_end() trace it too. > > Thus, I think the tracepoint might get an undesireble value.:) > > Thanks, > Yanfei > >>> BTW, remove an useless semicolon. >>> >>> Acked-by: David Hildenbrand <david@redhat.com> >>> Acked-by: Vlastimil Babka <vbabka@suse.cz> >>> Signed-off-by: Yanfei Xu <yanfei.xu@windriver.com> >>> --- >>> v1->v2: >>> Rename 'start_pfn' to 'iteration_start_pfn' and change commit messages. >>> >>> mm/compaction.c | 7 +++---- >>> 1 file changed, 3 insertions(+), 4 deletions(-) >>> >>> diff --git a/mm/compaction.c b/mm/compaction.c >>> index 176dcded298e..ccd27c739fd6 100644 >>> --- a/mm/compaction.c >>> +++ b/mm/compaction.c >>> @@ -2272,7 +2272,7 @@ compact_zone(struct compact_control *cc, struct >>> capture_control *capc) >>> while ((ret = compact_finished(cc)) == COMPACT_CONTINUE) { >>> int err; >>> - unsigned long start_pfn = cc->migrate_pfn; >>> + unsigned long iteration_start_pfn = cc->migrate_pfn; >>> /* >>> * Avoid multiple rescans which can happen if a page cannot be >>> @@ -2284,7 +2284,7 @@ compact_zone(struct compact_control *cc, struct >>> capture_control *capc) >>> */ >>> cc->rescan = false; >>> if (pageblock_start_pfn(last_migrated_pfn) == >>> - pageblock_start_pfn(start_pfn)) { >>> + pageblock_start_pfn(iteration_start_pfn)) { >>> cc->rescan = true; >>> } >>> @@ -2308,8 +2308,7 @@ compact_zone(struct compact_control *cc, struct >>> capture_control *capc) >>> goto check_drain; >>> case ISOLATE_SUCCESS: >>> update_cached = false; >>> - last_migrated_pfn = start_pfn; >>> - ; >>> + last_migrated_pfn = iteration_start_pfn; >>> } >>> err = migrate_pages(&cc->migratepages, compaction_alloc, >>> >> >> >
On 10/19/20 6:48 PM, Vlastimil Babka wrote: > On 10/19/20 12:29 PM, Xu, Yanfei wrote: >> >> >> On 10/19/20 5:40 PM, Vlastimil Babka wrote: >>> On 10/19/20 10:36 AM, yanfei.xu@windriver.com wrote: >>>> From: Yanfei Xu <yanfei.xu@windriver.com> >>>> >>>> There are two 'start_pfn' declared in compact_zone() which have >>>> different meaning. Rename the second one to 'iteration_start_pfn' >>>> to prevent trace_mm_compaction_end() from tracing an undesirable >>>> value. >>> >>> "to prevent confusion.", because trace_mm_compaction_end() has the >>> correct value even before the patch - the second start_pfn is out >>> of scope at that point. >>> >>> Thanks >>> >> In the while-statement, the second start_pfn is always be reassigned the >> value of cc->migrate_pfn in every loop, also the cc->migrate_pfn might >> be changed in the loop. Does trace_mm_compaction_end() really want to >> trace the new assinged start_pfn? > > compact_zone() > { > unsigned long start_pfn = cc->zone->zone_start_pfn; > > while ((ret = compact_finished(cc)) == COMPACT_CONTINUE) { > unsigned long start_pfn = cc->migrate_pfn; > ... > } > > trace_mm_compaction_end(start_pfn, cc->migrate_pfn, ...) > } > > Unless my C knowledge fails me completely, the start_pfn in the while > loop is a new different local variable that shadows the start_pfn from > compact_zone() level, but does not modify its value. After while loop > finishes, start_pfn has still the value assigned at > compact_zone() beginning and that's what tracepoint sees. > You are right! and I got your point. As you said, the second start_pfn is out of scope at that point. Will send v3. Many thanks, Yanfei > So renaming the variable in while loop is not a bug fix, but removing > confusion. > >> Without the patch： 566e54e11（mm, compaction: remove last_migrated_pfn >> from compact_control）, there is only one start_pfn which has a fixed >> value. The trace_mm_compaction_end() trace it too. >> >> Thus, I think the tracepoint might get an undesireble value.:) >> >> Thanks, >> Yanfei >> >>>> BTW, remove an useless semicolon. >>>> >>>> Acked-by: David Hildenbrand <david@redhat.com> >>>> Acked-by: Vlastimil Babka <vbabka@suse.cz> >>>> Signed-off-by: Yanfei Xu <yanfei.xu@windriver.com> >>>> --- >>>> v1->v2: >>>> Rename 'start_pfn' to 'iteration_start_pfn' and change commit messages. >>>> >>>> mm/compaction.c | 7 +++---- >>>> 1 file changed, 3 insertions(+), 4 deletions(-) >>>> >>>> diff --git a/mm/compaction.c b/mm/compaction.c >>>> index 176dcded298e..ccd27c739fd6 100644 >>>> --- a/mm/compaction.c >>>> +++ b/mm/compaction.c >>>> @@ -2272,7 +2272,7 @@ compact_zone(struct compact_control *cc, >>>> struct capture_control *capc) >>>> while ((ret = compact_finished(cc)) == COMPACT_CONTINUE) { >>>> int err; >>>> - unsigned long start_pfn = cc->migrate_pfn; >>>> + unsigned long iteration_start_pfn = cc->migrate_pfn; >>>> /* >>>> * Avoid multiple rescans which can happen if a page >>>> cannot be >>>> @@ -2284,7 +2284,7 @@ compact_zone(struct compact_control *cc, >>>> struct capture_control *capc) >>>> */ >>>> cc->rescan = false; >>>> if (pageblock_start_pfn(last_migrated_pfn) == >>>> - pageblock_start_pfn(start_pfn)) { >>>> + pageblock_start_pfn(iteration_start_pfn)) { >>>> cc->rescan = true; >>>> } >>>> @@ -2308,8 +2308,7 @@ compact_zone(struct compact_control *cc, >>>> struct capture_control *capc) >>>> goto check_drain; >>>> case ISOLATE_SUCCESS: >>>> update_cached = false; >>>> - last_migrated_pfn = start_pfn; >>>> - ; >>>> + last_migrated_pfn = iteration_start_pfn; >>>> } >>>> err = migrate_pages(&cc->migratepages, compaction_alloc, >>>> >>> >>> >> >
diff --git a/mm/compaction.c b/mm/compaction.c index 176dcded298e..ccd27c739fd6 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -2272,7 +2272,7 @@ compact_zone(struct compact_control *cc, struct capture_control *capc) while ((ret = compact_finished(cc)) == COMPACT_CONTINUE) { int err; - unsigned long start_pfn = cc->migrate_pfn; + unsigned long iteration_start_pfn = cc->migrate_pfn; /* * Avoid multiple rescans which can happen if a page cannot be @@ -2284,7 +2284,7 @@ compact_zone(struct compact_control *cc, struct capture_control *capc) */ cc->rescan = false; if (pageblock_start_pfn(last_migrated_pfn) == - pageblock_start_pfn(start_pfn)) { + pageblock_start_pfn(iteration_start_pfn)) { cc->rescan = true; } @@ -2308,8 +2308,7 @@ compact_zone(struct compact_control *cc, struct capture_control *capc) goto check_drain; case ISOLATE_SUCCESS: update_cached = false; - last_migrated_pfn = start_pfn; - ; + last_migrated_pfn = iteration_start_pfn; } err = migrate_pages(&cc->migratepages, compaction_alloc,