On 11/24/2014 03:54 PM, Dexuan Cui wrote: >> -----Original Message----- >> From: Jason Wang [mailto:jasowang@xxxxxxxxxx] >> Sent: Monday, November 24, 2014 15:28 PM >> To: Dexuan Cui; gregkh@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; >> driverdev-devel@xxxxxxxxxxxxxxxxxxxxxx; olaf@xxxxxxxxx; >> apw@xxxxxxxxxxxxx; KY Srinivasan >> Cc: Haiyang Zhang >> Subject: Re: [PATCH] hv: hv_balloon: avoid memory leak on alloc_error of >> 2MB memory block >> >> On 11/24/2014 02:08 PM, Dexuan Cui wrote: >>>> -----Original Message----- >>>>> From: Jason Wang [mailto:jasowang@xxxxxxxxxx] >>>>> Sent: Monday, November 24, 2014 13:18 PM >>>>> To: Dexuan Cui; gregkh@xxxxxxxxxxxxxxxxxxx; linux- >> kernel@xxxxxxxxxxxxxxx; >>>>> driverdev-devel@xxxxxxxxxxxxxxxxxxxxxx; olaf@xxxxxxxxx; >>>>> apw@xxxxxxxxxxxxx; KY Srinivasan >>>>> Cc: Haiyang Zhang >>>>> Subject: Re: [PATCH] hv: hv_balloon: avoid memory leak on >> alloc_error of >>>>> 2MB memory block >>>>> >>>>> On 11/24/2014 01:56 PM, Dexuan Cui wrote: >>>>>>> If num_ballooned is not 0, we shouldn't neglect the already- >> allocated >>>>> 2MB >>>>>>> memory block(s). >>>>>>> >>>>>>> Cc: K. Y. Srinivasan <kys@xxxxxxxxxxxxx> >>>>>>> Cc: <stable@xxxxxxxxxxxxxxx> >>>>>>> Signed-off-by: Dexuan Cui <decui@xxxxxxxxxxxxx> >>>>>>> --- >>>>>>> drivers/hv/hv_balloon.c | 4 +++- >>>>>>> 1 file changed, 3 insertions(+), 1 deletion(-) >>>>>>> >>>>>>> diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c >>>>>>> index 5e90c5d..cba2d3b 100644 >>>>>>> --- a/drivers/hv/hv_balloon.c >>>>>>> +++ b/drivers/hv/hv_balloon.c >>>>>>> @@ -1091,6 +1091,8 @@ static void balloon_up(struct >> work_struct >>>>> *dummy) >>>>>>> bool done = false; >>>>>>> int i; >>>>>>> >>>>>>> + /* The host does balloon_up in 2MB. */ >>>>>>> + WARN_ON(num_pages % PAGES_IN_2M != 0); >>>>>>> >>>>>>> /* >>>>>>> * We will attempt 2M allocations. However, if we fail to >>>>>>> @@ -1111,7 +1113,7 @@ static void balloon_up(struct >> work_struct >>>>> *dummy) >>>>>>> bl_resp, alloc_unit, >>>>>>> &alloc_error); >>>>>>> >>>>>>> - if ((alloc_error) && (alloc_unit != 1)) { >>>>>>> + if (alloc_error && (alloc_unit != 1) && >> num_ballooned == 0) >>>>> { >>>>>>> alloc_unit = 1; >>>>>>> continue; >>>>>>> } >>>>> Before the change, we may retry the 4K allocation when part or all 2M >>>>> allocations were failed. This makes sense when memory is fragmented. >> But >>> Yes, but all the partially-allocated 2MB memory blocks are lost(mem leak). >>> >>>>> after the change, if part of 2M allocation were failed, we won't retry >>>>> 4K allocation. Is this expected? >>> Hi Jason, >>> The patch doesn't break the "try 2MB first; then try 4K" logic: >>> >>> With the change, we'll retry the 2MB allocation in the next iteration of the >>> same while (!done) loop -- we expect this retry will cause >>> "alloc_error && (alloc_unit != 1) && num_ballooned == 0" to be true, >>> so we'll later try 4K allocation, as we did before. >> If I read the code correctly, if part of 2M allocation fails. >> alloc_balloon_pages() will have a non zero return value with alloc_error >> set. Then it will match the following check: >> >> if ((alloc_error) || (num_ballooned == num_pages)) >> { >> >> which will set done to true. So there's no second iteration of while >> (!done) loop? > Oh... I see the issue in my patch. > Thanks for pointing this out, Jason! > >> Probably you need something like: >> >> if ((alloc_unit != 1) && (num_ballooned == 0)) { >> alloc_unit = 1; >> continue; >> } >> >> if ((alloc_unit == 1) || (num_ballooned == num_pages)) { >> ... >> } > Your code is good, except for one thing: > alloc_balloon_pages() can return due to: > > if (bl_resp->hdr.size + sizeof(union dm_mem_page_range) > > PAGE_SIZE) > return i * alloc_unit; > > In this case, "alloc_unit == 1" is true, but we shouldn't run "done = true". > > How do you like this? I made a few changes based on your code. > > @@ -1086,16 +1088,18 @@ static void balloon_up(struct work_struct *dummy) > num_pages -= num_ballooned; > + alloc_error = false; > num_ballooned = alloc_balloon_pages(&dm_device, num_pages, > bl_resp, alloc_unit, > &alloc_error); > > - if ((alloc_error) && (alloc_unit != 1)) { > + if (alloc_unit != 1 && num_ballooned == 0) { > alloc_unit = 1; > continue; > } > > - if ((alloc_error) || (num_ballooned == num_pages)) { > + if ((alloc_unit == 1 && alloc_error) || > + (num_ballooned == num_pages)) { > bl_resp->more_pages = 0; > done = true; > dm_device.state = DM_INITIALIZED; > > > If you're Ok with this, I'll send out a v2 patch. > > Thanks, > -- Dexuan Looks good. Thanks _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
