| Message ID | 20220329132619.18689-2-linmiaohe@huawei.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | A few cleanup and fixup patches for migration | expand |
On Tue, Mar 29, 2022 at 09:26:12PM +0800, Miaohe Lin wrote: > When folio is file lru, folio_test_swapbacked is guaranteed to be true. So > it's unnecessary to check it here again. No functional change intended. ummm ... is your logic right here? The condition is: if (!a || (b && !c)) I don't see how it follows that a => c means we can do any simplification at all. > Signed-off-by: Miaohe Lin <linmiaohe@huawei.com> > --- > mm/vmscan.c | 3 +-- > 1 file changed, 1 insertion(+), 2 deletions(-) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index 1678802e03e7..7c1a9713bfc9 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -1434,8 +1434,7 @@ static void folio_check_dirty_writeback(struct folio *folio, > * Anonymous pages are not handled by flushers and must be written > * from reclaim context. Do not stall reclaim based on them > */ > - if (!folio_is_file_lru(folio) || > - (folio_test_anon(folio) && !folio_test_swapbacked(folio))) { > + if (!folio_is_file_lru(folio) || folio_test_anon(folio)) { > *dirty = false; > *writeback = false; > return; > -- > 2.23.0 > >
On 2022/3/29 21:46, Matthew Wilcox wrote: > On Tue, Mar 29, 2022 at 09:26:12PM +0800, Miaohe Lin wrote: >> When folio is file lru, folio_test_swapbacked is guaranteed to be true. So >> it's unnecessary to check it here again. No functional change intended. > > ummm ... is your logic right here? The condition is: > > if (!a || (b && !c)) > Because a is !c, so c is !a. Then we have: !a || (b && !c) ==> !a || (b && !!a) ==> !a || (b && a) ==> !a || b. Or am I miss something? Thanks. > I don't see how it follows that a => c means we can do any > simplification at all. > >> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com> >> --- >> mm/vmscan.c | 3 +-- >> 1 file changed, 1 insertion(+), 2 deletions(-) >> >> diff --git a/mm/vmscan.c b/mm/vmscan.c >> index 1678802e03e7..7c1a9713bfc9 100644 >> --- a/mm/vmscan.c >> +++ b/mm/vmscan.c >> @@ -1434,8 +1434,7 @@ static void folio_check_dirty_writeback(struct folio *folio, >> * Anonymous pages are not handled by flushers and must be written >> * from reclaim context. Do not stall reclaim based on them >> */ >> - if (!folio_is_file_lru(folio) || >> - (folio_test_anon(folio) && !folio_test_swapbacked(folio))) { >> + if (!folio_is_file_lru(folio) || folio_test_anon(folio)) { >> *dirty = false; >> *writeback = false; >> return; >> -- >> 2.23.0 >> >> > > . >
On Tue, Mar 29, 2022 at 9:26 PM Miaohe Lin <linmiaohe@huawei.com> wrote: > > When folio is file lru, folio_test_swapbacked is guaranteed to be true. So > it's unnecessary to check it here again. No functional change intended. > > Signed-off-by: Miaohe Lin <linmiaohe@huawei.com> > --- > mm/vmscan.c | 3 +-- > 1 file changed, 1 insertion(+), 2 deletions(-) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index 1678802e03e7..7c1a9713bfc9 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -1434,8 +1434,7 @@ static void folio_check_dirty_writeback(struct folio *folio, > * Anonymous pages are not handled by flushers and must be written > * from reclaim context. Do not stall reclaim based on them > */ > - if (!folio_is_file_lru(folio) || > - (folio_test_anon(folio) && !folio_test_swapbacked(folio))) { > + if (!folio_is_file_lru(folio) || folio_test_anon(folio)) { At least your login is no problem since folio_is_file_lru() is equal to !folio_test_swapbacked(). But the new code is not clear to me. The old code is easy to understand, e.g. folio_test_anon(folio) && !folio_test_swapbacked(folio) tells us that the anon pages which do not need to be swapped should be skipped. So I'm neutral on the patch.
On 2022/3/30 16:13, Muchun Song wrote: > On Tue, Mar 29, 2022 at 9:26 PM Miaohe Lin <linmiaohe@huawei.com> wrote: >> >> When folio is file lru, folio_test_swapbacked is guaranteed to be true. So >> it's unnecessary to check it here again. No functional change intended. >> >> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com> >> --- >> mm/vmscan.c | 3 +-- >> 1 file changed, 1 insertion(+), 2 deletions(-) >> >> diff --git a/mm/vmscan.c b/mm/vmscan.c >> index 1678802e03e7..7c1a9713bfc9 100644 >> --- a/mm/vmscan.c >> +++ b/mm/vmscan.c >> @@ -1434,8 +1434,7 @@ static void folio_check_dirty_writeback(struct folio *folio, >> * Anonymous pages are not handled by flushers and must be written >> * from reclaim context. Do not stall reclaim based on them >> */ >> - if (!folio_is_file_lru(folio) || >> - (folio_test_anon(folio) && !folio_test_swapbacked(folio))) { >> + if (!folio_is_file_lru(folio) || folio_test_anon(folio)) { > > At least your login is no problem since folio_is_file_lru() is equal to > !folio_test_swapbacked(). But the new code is not clear to me. > The old code is easy to understand, e.g. folio_test_anon(folio) && > !folio_test_swapbacked(folio) tells us that the anon pages which > do not need to be swapped should be skipped. So I'm neutral on > the patch. Thanks for your comment. The previous one might look more common: folio_test_anon(folio) && !folio_test_swapbacked(folio) means folio is MADV_FREE and can be freed without swapping out. And I remove the unneeded !folio_test_swapbacked(folio) check at the expense of losing minor readability. If it is not worth doing this, I will drop this patch. Thanks. > > . >
Muchun Song <songmuchun@bytedance.com> writes: > On Tue, Mar 29, 2022 at 9:26 PM Miaohe Lin <linmiaohe@huawei.com> wrote: >> >> When folio is file lru, folio_test_swapbacked is guaranteed to be true. So >> it's unnecessary to check it here again. No functional change intended. >> >> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com> >> --- >> mm/vmscan.c | 3 +-- >> 1 file changed, 1 insertion(+), 2 deletions(-) >> >> diff --git a/mm/vmscan.c b/mm/vmscan.c >> index 1678802e03e7..7c1a9713bfc9 100644 >> --- a/mm/vmscan.c >> +++ b/mm/vmscan.c >> @@ -1434,8 +1434,7 @@ static void folio_check_dirty_writeback(struct folio *folio, >> * Anonymous pages are not handled by flushers and must be written >> * from reclaim context. Do not stall reclaim based on them >> */ >> - if (!folio_is_file_lru(folio) || >> - (folio_test_anon(folio) && !folio_test_swapbacked(folio))) { >> + if (!folio_is_file_lru(folio) || folio_test_anon(folio)) { > > At least your login is no problem since folio_is_file_lru() is equal to > !folio_test_swapbacked(). But the new code is not clear to me. > The old code is easy to understand, e.g. folio_test_anon(folio) && > !folio_test_swapbacked(folio) tells us that the anon pages which > do not need to be swapped should be skipped. That is for MADV_FREE pages. The code is introduced in commit 802a3a92ad7a ("mm: reclaim MADV_FREE pages"). So I think the original code is better. It's an implementation detail that folio_is_file_lru() equals !folio_test_swapbacked(). It may be better to add some comments here for MADV_FREE pages. > So I'm neutral on the patch. Best Regards, Huang, Ying
On 2022/3/31 14:37, Huang, Ying wrote: > Muchun Song <songmuchun@bytedance.com> writes: > >> On Tue, Mar 29, 2022 at 9:26 PM Miaohe Lin <linmiaohe@huawei.com> wrote: >>> >>> When folio is file lru, folio_test_swapbacked is guaranteed to be true. So >>> it's unnecessary to check it here again. No functional change intended. >>> >>> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com> >>> --- >>> mm/vmscan.c | 3 +-- >>> 1 file changed, 1 insertion(+), 2 deletions(-) >>> >>> diff --git a/mm/vmscan.c b/mm/vmscan.c >>> index 1678802e03e7..7c1a9713bfc9 100644 >>> --- a/mm/vmscan.c >>> +++ b/mm/vmscan.c >>> @@ -1434,8 +1434,7 @@ static void folio_check_dirty_writeback(struct folio *folio, >>> * Anonymous pages are not handled by flushers and must be written >>> * from reclaim context. Do not stall reclaim based on them >>> */ >>> - if (!folio_is_file_lru(folio) || >>> - (folio_test_anon(folio) && !folio_test_swapbacked(folio))) { >>> + if (!folio_is_file_lru(folio) || folio_test_anon(folio)) { >> >> At least your login is no problem since folio_is_file_lru() is equal to >> !folio_test_swapbacked(). But the new code is not clear to me. >> The old code is easy to understand, e.g. folio_test_anon(folio) && >> !folio_test_swapbacked(folio) tells us that the anon pages which >> do not need to be swapped should be skipped. > > That is for MADV_FREE pages. The code is introduced in commit > 802a3a92ad7a ("mm: reclaim MADV_FREE pages"). > > So I think the original code is better. It's an implementation detail > that folio_is_file_lru() equals !folio_test_swapbacked(). It may be > better to add some comments here for MADV_FREE pages. > Do you tend to drop this patch or adding a comment with the change in this patch or something else? Thanks. >> So I'm neutral on the patch. > > Best Regards, > Huang, Ying > . >
Miaohe Lin <linmiaohe@huawei.com> writes: > On 2022/3/31 14:37, Huang, Ying wrote: >> Muchun Song <songmuchun@bytedance.com> writes: >> >>> On Tue, Mar 29, 2022 at 9:26 PM Miaohe Lin <linmiaohe@huawei.com> wrote: >>>> >>>> When folio is file lru, folio_test_swapbacked is guaranteed to be true. So >>>> it's unnecessary to check it here again. No functional change intended. >>>> >>>> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com> >>>> --- >>>> mm/vmscan.c | 3 +-- >>>> 1 file changed, 1 insertion(+), 2 deletions(-) >>>> >>>> diff --git a/mm/vmscan.c b/mm/vmscan.c >>>> index 1678802e03e7..7c1a9713bfc9 100644 >>>> --- a/mm/vmscan.c >>>> +++ b/mm/vmscan.c >>>> @@ -1434,8 +1434,7 @@ static void folio_check_dirty_writeback(struct folio *folio, >>>> * Anonymous pages are not handled by flushers and must be written >>>> * from reclaim context. Do not stall reclaim based on them >>>> */ >>>> - if (!folio_is_file_lru(folio) || >>>> - (folio_test_anon(folio) && !folio_test_swapbacked(folio))) { >>>> + if (!folio_is_file_lru(folio) || folio_test_anon(folio)) { >>> >>> At least your login is no problem since folio_is_file_lru() is equal to >>> !folio_test_swapbacked(). But the new code is not clear to me. >>> The old code is easy to understand, e.g. folio_test_anon(folio) && >>> !folio_test_swapbacked(folio) tells us that the anon pages which >>> do not need to be swapped should be skipped. >> >> That is for MADV_FREE pages. The code is introduced in commit >> 802a3a92ad7a ("mm: reclaim MADV_FREE pages"). >> >> So I think the original code is better. It's an implementation detail >> that folio_is_file_lru() equals !folio_test_swapbacked(). It may be >> better to add some comments here for MADV_FREE pages. >> > > Do you tend to drop this patch or adding a comment with the change in this patch or something else? I suggest to drop the code change and add a comment about MADV_FREE. Best Regards, Huang, Ying > Thanks. > >>> So I'm neutral on the patch. >> >> Best Regards, >> Huang, Ying >> . >>
On 2022/3/31 16:02, Huang, Ying wrote: > Miaohe Lin <linmiaohe@huawei.com> writes: > >> On 2022/3/31 14:37, Huang, Ying wrote: >>> Muchun Song <songmuchun@bytedance.com> writes: >>> >>>> On Tue, Mar 29, 2022 at 9:26 PM Miaohe Lin <linmiaohe@huawei.com> wrote: >>>>> >>>>> When folio is file lru, folio_test_swapbacked is guaranteed to be true. So >>>>> it's unnecessary to check it here again. No functional change intended. >>>>> >>>>> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com> >>>>> --- >>>>> mm/vmscan.c | 3 +-- >>>>> 1 file changed, 1 insertion(+), 2 deletions(-) >>>>> >>>>> diff --git a/mm/vmscan.c b/mm/vmscan.c >>>>> index 1678802e03e7..7c1a9713bfc9 100644 >>>>> --- a/mm/vmscan.c >>>>> +++ b/mm/vmscan.c >>>>> @@ -1434,8 +1434,7 @@ static void folio_check_dirty_writeback(struct folio *folio, >>>>> * Anonymous pages are not handled by flushers and must be written >>>>> * from reclaim context. Do not stall reclaim based on them >>>>> */ >>>>> - if (!folio_is_file_lru(folio) || >>>>> - (folio_test_anon(folio) && !folio_test_swapbacked(folio))) { >>>>> + if (!folio_is_file_lru(folio) || folio_test_anon(folio)) { >>>> >>>> At least your login is no problem since folio_is_file_lru() is equal to >>>> !folio_test_swapbacked(). But the new code is not clear to me. >>>> The old code is easy to understand, e.g. folio_test_anon(folio) && >>>> !folio_test_swapbacked(folio) tells us that the anon pages which >>>> do not need to be swapped should be skipped. >>> >>> That is for MADV_FREE pages. The code is introduced in commit >>> 802a3a92ad7a ("mm: reclaim MADV_FREE pages"). >>> >>> So I think the original code is better. It's an implementation detail >>> that folio_is_file_lru() equals !folio_test_swapbacked(). It may be >>> better to add some comments here for MADV_FREE pages. >>> >> >> Do you tend to drop this patch or adding a comment with the change in this patch or something else? > > I suggest to drop the code change and add a comment about MADV_FREE. Will do. Thanks. > > Best Regards, > Huang, Ying > >> Thanks. >> >>>> So I'm neutral on the patch. >>> >>> Best Regards, >>> Huang, Ying >>> . >>> > . >
diff --git a/mm/vmscan.c b/mm/vmscan.c index 1678802e03e7..7c1a9713bfc9 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -1434,8 +1434,7 @@ static void folio_check_dirty_writeback(struct folio *folio, * Anonymous pages are not handled by flushers and must be written * from reclaim context. Do not stall reclaim based on them */ - if (!folio_is_file_lru(folio) || - (folio_test_anon(folio) && !folio_test_swapbacked(folio))) { + if (!folio_is_file_lru(folio) || folio_test_anon(folio)) { *dirty = false; *writeback = false; return;
When folio is file lru, folio_test_swapbacked is guaranteed to be true. So it's unnecessary to check it here again. No functional change intended. Signed-off-by: Miaohe Lin <linmiaohe@huawei.com> --- mm/vmscan.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-)