On Sat 03-06-17 10:24:40, Wei Yang wrote: > Hi, Michal > > Just go through your patch. > > I have one question and one suggestion as below. > > One suggestion: > > This patch does two things to me: > 1. Replace __GFP_REPEAT with __GFP_RETRY_MAYFAIL > 2. Adjust the logic in page_alloc to provide the middle semantic > > My suggestion is to split these two task into two patches, so that readers > could catch your fundamental logic change easily. Well, the rename and the change is intentionally tight together. My previous patches have removed all __GFP_REPEAT users for low order requests which didn't have any implemented semantic. So as of now we should only have those users which semantic will not change. I do not add any new low order user in this patch so it in fact doesn't change any existing semnatic. > > On Tue, Mar 07, 2017 at 04:48:41PM +0100, Michal Hocko wrote: > >From: Michal Hocko <mhocko@xxxxxxxx> [...] > >@@ -3776,9 +3784,9 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order, > > > > /* > > * Do not retry costly high order allocations unless they are > >- * __GFP_REPEAT > >+ * __GFP_RETRY_MAYFAIL > > */ > >- if (order > PAGE_ALLOC_COSTLY_ORDER && !(gfp_mask & __GFP_REPEAT)) > >+ if (order > PAGE_ALLOC_COSTLY_ORDER && !(gfp_mask & __GFP_RETRY_MAYFAIL)) > > goto nopage; > > One question: > > From your change log, it mentions will provide the same semantic for !costly > allocations. While the logic here is the same as before. > > For a !costly allocation with __GFP_REPEAT flag, the difference after this > patch is no OOM will be invoked, while it will still continue in the loop. Not really. There are two things. The above will shortcut retrying if there is _no_ __GFP_RETRY_MAYFAIL. If the flags _is_ specified we will back of in __alloc_pages_may_oom. > Maybe I don't catch your point in this message: > > __GFP_REPEAT was designed to allow retry-but-eventually-fail semantic to > the page allocator. This has been true but only for allocations requests > larger than PAGE_ALLOC_COSTLY_ORDER. It has been always ignored for > smaller sizes. This is a bit unfortunate because there is no way to > express the same semantic for those requests and they are considered too > important to fail so they might end up looping in the page allocator for > ever, similarly to GFP_NOFAIL requests. > > I thought you will provide the same semantic to !costly allocation, or I > misunderstand? yes and that is the case. __alloc_pages_may_oom will back off before OOM killer is invoked and the allocator slow path will fail because did_some_progress == 0; -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
